Aluminosilicate Glasses

ABSTRACT

Compounds, compositions, articles, devices, and methods for the manufacture of light guide plates and back light units including such light guide plates made from glass. In some embodiments, light guide plates (LGPs) are provided that have similar or superior optical properties to light guide plates made from PMMA and that have exceptional mechanical properties such as rigidity, CTE and dimensional stability in high moisture conditions as compared to PMMA light guide plates.

This application is a continuation application of co-pending U.S.application Ser. No. 14/734,707 filed Jun. 9, 2015, which claims thebenefit of priority to U.S. Provisional Application No. 62/132,258 filedMar. 12, 2015, to U.S. Provisional Application No. 62/114,825 filed Feb.11, 2015, to U.S. Provisional Application No. 62/026,264 filed Jul. 18,2014 and to U.S. Provisional Application No. 62/014,382 filed Jun. 19,2014 the content of each are incorporated herein by reference in theirentirety.

BACKGROUND

Side lit back light units include a light guide plate (LGP) that isusually made of high transmission plastic materials such aspolymethylmethacrylate (PMMA). Although such plastic materials presentexcellent properties such as light transmission, these materials exhibitrelatively poor mechanical properties such as rigidity, coefficient ofthermal expansion (CTE) and moisture absorption.

Accordingly, it would be desirable to provide an improved light guideplate having attributes that achieve an improved optical performance interms of light transmission, scattering and light coupling as well asexhibiting exceptional mechanical performance in terms of rigidity, CTE,and moisture absorption.

SUMMARY

Aspects of the subject matter pertain to compounds, compositions,articles, devices, and methods for the manufacture of light guide platesand back light units including such light guide plates made from glass.In some embodiments, light guide plates (LGPs) are provided that havesimilar or superior optical properties to light guide plates made fromPMMA and that have exceptional mechanical properties such as rigidity,CTE and dimensional stability in high moisture conditions as compared toPMMA light guide plates.

Principles and embodiments of the present subject matter relate in someembodiments to a light guide plate for use in a backlight unit,comprising a glass sheet with a front face having a width and a height,a back face opposite the front face, and a thickness between the frontface and back face, forming four edges around the front and back faces,wherein the roughness of at least one face is less than 0.6 nm, andwherein the glass of the glass plate comprises between 50-80 mol % SiO₂,between 0-20 mol % Al₂O₃, and between 0-25 mol % B₂O₃, and less than 50ppm iron (Fe) concentration. Additional embodiments relate to a glassarticle that can be used in display devices, in lighting applicationsand/or in architectural applications.

In various embodiments, the thickness of the plate is less than 1.5% ofthe front face height. Some embodiments also relate to a light guideplate where the thickness has a variation of less than 5%. In variousembodiments, the light guide plate is obtained from a fusion drawprocess. In various embodiments, the light guide plate is obtained froma float glass process. Embodiments of the present subject matter alsorelate to a light guide plate where at least 10% of the iron is Fe²⁺.Additional embodiments of the present subject matter relate to a lightguide plate where greater than 20% of the iron is Fe²⁺. Furtherembodiments relate to a light guide plate where the glass comprises lessthan 1 ppm of Co, Ni, and Cr. Embodiments of the present subject matteralso relate to a light guide plate where the glass further comprisesR_(x)O where R is Li, Na, K, Rb, Cs, and x is 2, or R is Mg, Ca, Sr orBa, and x is 1, and the mol % of R_(x)O is approximately equal to themol % of Al₂O₃. Additional embodiments relate to a light guide platewhere at least one edge is a light injection edge that scatters lightwithin an angle less than 12.8 degrees full width half maximum (FWHM) intransmission.

Some embodiments relate to a light guide plate where thermal conductionof the light guide plate is greater than 0.5 W/m/K. Further embodimentsrelate to a light guide plate where the light injection edge is obtainedby grinding the edge without polishing the light injection edge.Additional embodiments relate to a light guide plate where the glasssheet further comprises a second edge adjacent to the light injectionedge and a third edge opposite the second edge and adjacent to the lightinjection edge, wherein the second edge and the third edge scatter lightwithin an angle of less than 12.8 degrees FWHM in reflection. In someembodiments a light guide plate is provided where the second edge andthe third edge have a diffusion angle in reflection that is below 6.4degrees.

Principles and embodiments of the present subject matter also relate toa method of making a light guide plate for use in a backlight unit,comprising forming a glass sheet and filtering out ultraviolet lightduring processing of the glass sheet to prevent exposure of the glasssheet to ultraviolet light. Embodiments also relate to a light guideplate where the glass sheet is formed by a float glass process followedby polishing or where the glass sheet is formed by a fusion drawprocess. In some embodiments, a first edge of an exemplary apparatus maybe grinded to provide a light injection edge and/or two edges adjacentthe first light injection edge may also be grinded wherein the lightinjection edge and the two edges adjacent the LED injection edge are notpolished.

Some embodiments comprise a glass article, comprising a glass sheet witha front face having a width and a height, a back face opposite the frontface, and a thickness between the front face and back face, forming fouredges around the front and back faces, wherein the glass sheet comprisesbetween about 50 mol % to about 90 mol % SiO₂, between about 0 mol % toabout 20 mol % Al₂O₃, 0 mol % to about 20 mol % B₂O₃, and about 0 mol %to about 25 mol % R_(x)O, wherein R is any one or more of Li, Na, K, Rb,Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the glassproduces less than or equal to 2 dB/500 mm absorption. In furtherembodiments, R_(x)O—Al₂O₃>0; 0<R_(x)O—Al₂O₃<15; x=2 and R₂O—Al₂O₃<15;R₂O—Al₂O₃<2; x=2 and R₂O—Al₂O₃—MgO>−15; 0<(R_(x)O—Al₂O₃)<25,−11<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃—MgO)<11; and/or −1<(R₂O—Al₂O₃)<2and −6<(R₂O—Al₂O₃—MgO)<1. In other embodiments, the glass article is alight guide plate. In some embodiments, a roughness of at least one faceis less than 0.6 nm. In additional embodiments, the thickness of theplate is between about 0.5 mm and about 8 mm. In further embodiments,the thickness has a variation of less than 5%. In some embodiments, thelight guide plate is manufactured from a fusion draw process, slot drawprocess, or a float process. In further embodiments, at least 10% of theiron is Fe²⁺. In some embodiments, the glass article has a liquidusviscosity greater than 100 kP and a T_(200P) temperature below 1760° C.In some embodiments, the glass comprises less than 1 ppm each of Co, Ni,and Cr. In some embodiments, the concentration of Fe is <about 50 ppm,<about 20 ppm, or <about 10 ppm. In other embodiments,Fe+30Cr+35Ni<about 60 ppm, Fe+30Cr+35Ni<about 40 ppm, Fe+30Cr+35Ni<about20 ppm, or Fe+30Cr+35Ni<about 10 ppm. In some embodiments, at least oneedge is a light injection edge (polished or unpolished) that scatterslight within an angle less than 12.8 degrees full width half maximum(FWHM) in transmission. In some embodiments, the glass sheet furthercomprises a second edge adjacent to the light injection edge and a thirdedge opposite the second edge and adjacent to the light injection edge,wherein the second edge and the third edge scatter light within an angleof less than 12.8 degrees FWHM in reflection. The second edge and thethird edge can have a diffusion angle in reflection that is below 6.4degrees. In some embodiments, the transmittance at 450 nm with at least500 mm in length is greater than or equal to 85%, the transmittance at550 nm with at least 500 mm in length is greater than or equal to 90%,or the transmittance at 630 nm with at least 500 mm in length is greaterthan or equal to 85%, and combinations thereof. In some embodiments, thedensity is between about 1.95 gm/cc @ 20 C to about 2.7 gm/cc @ 20 C,the Young's modulus is between about 62 GPa to about 90 GPa, and/or theCTE (0-300° C.) is between about 30×10-7/° C. to about 95×10-7/° C. Insome embodiments, the glass sheet is chemically strengthened. In someembodiments, T_(200P) temperature is below 1760° C., below 1730° C. orbelow 1700° C. In some embodiments, a liquidus viscosity can be greaterthan 100 kP or greater than 500kP.

In additional embodiments, a glass article is provided comprising aglass sheet with a front face having a width and a height, a back faceopposite the front face, and a thickness between the front face and backface, forming four edges around the front and back faces, wherein theglass sheet comprises between about 60 mol % to about 80 mol % SiO₂,between about 0.1 mol % to about 15 mol % Al₂O₃, 0 mol % to about 12 mol% B₂O₃, and about 0.1 mol % to about 15 mol % R2O and about 0.1 mol % toabout 15 mol % RO, wherein R is any one or more of Li, Na, K, Rb, Cs andx is 2, or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the glassproduces less than or equal to 2 dB/500 mm absorption. In someembodiments, Fe+30Cr+35Ni<about 60 ppm, Fe+30Cr+35Ni<about 40 ppm,Fe+30Cr+35Ni<about 30 ppm, or Fe+30Cr+35Ni<about 20 ppm. In someembodiments, 0<(R_(x)O—Al₂O₃)<25, −11<(R₂O—Al₂O₃)<11, and−15<(R₂O—Al₂O₃—MgO)<11. In some embodiments, the glass produces lessthan or equal to 0.5 dB/500 mm absorption or less than or equal to 0.25dB/500 mm absorption.

In further embodiments, a glass article is provided comprising a glasssheet having between about 50 mol % to about 90 mol % SiO₂, betweenabout 0 mol % to about 15 mol % Al₂O₃, between about 0 mol % to about 12mol % B₂O₃, and about 2 mol % to about 25 mol % R_(x)O, wherein R is anyone or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba andx is 1, and wherein Fe+30Cr+35Ni<about 60 ppm.

In additional embodiments, a light guide plate is provided comprising aglass sheet having between about 0 mol % to about 15 mol % Al₂O₃, andabout 0 mol % to about 25 mol % R_(x)O, wherein R is any one or more ofLi, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1, andwherein Fe is <about 50 ppm. In some embodiments, the light guide platefurther comprises between about 50 mol % to about 90 mol % SiO₂ andbetween about 0 mol % to about 12 mol % B₂O₃. In some embodiments, theglass comprises less than 1 ppm of each of Co, Ni, and Cr. In someembodiments, the glass produces less than or equal to 2 dB/500 mm oflight attenuation, less than or equal to 1 dB/500 mm absorption, or lessthan or equal to 0.5 dB/500 mm absorption. In other embodiments,Fe+30Cr+35Ni<about 60 ppm or Fe+30Cr+35Ni<about 20 ppm. In someembodiments, the mol % of Al₂O₃ is <or substantially equal to the mol %R_(x)O; R_(x)O—Al₂O₃>0; 0<R_(x)O—Al₂O₃<25; x=2 and R₂O—Al₂O₃<15;R₂O—Al₂O₃<2; x=2 and R₂O—Al₂O₃—MgO>−15. In some embodiments,0<(R_(x)O—Al₂O₃)<25, −11<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃—MgO)<11. Insome embodiments, −1<(R₂O—Al₂O₃)<2 and −6<(R₂O—Al₂O₃—MgO)<1. In someembodiments, the transmittance at 450 nm with at least 500 mm in lengthis greater than or equal to 85%, the transmittance at 550 nm with atleast 500 mm in length is greater than or equal to 90%, or thetransmittance at 630 nm with at least 500 mm in length is greater thanor equal to 85%, and combinations thereof. In some embodiments, theconcentration of Fe is <about 20 ppm or the concentration of Fe is<about 10 ppm. In some embodiments, the glass sheet is chemicallystrengthened. In further embodiments, a display device comprises thelight guide plate described above wherein the light guide plate furthercomprises a glass sheet with a front face having a width and a height, aback face opposite the front face, and a thickness between the frontface and back face, forming four edges around the front and back faces,and wherein one or more edges of the light guide plate are illuminatedby a light source. The light source can be selected from the groupconsisting of an LED, CCFL, OLED, and combinations thereof. The displaydevice can have glass comprising less than 1 ppm of each of Co, Ni, andCr. This glass can produce less than or equal to 2 dB/500 mm of lightattenuation. In some embodiments, Fe+30Cr+35Ni<about 60 ppm and/or themol % of Al₂O₃ is <or substantially equal to the mol % R_(x)O. In someembodiments, the thickness of the display device is less than 5 mm. Insome embodiments, the transmittance at 450 nm with at least 500 mm inlength is greater than or equal to 85%, the transmittance at 550 nm withat least 500 mm in length is greater than or equal to 90%, or thetransmittance at 630 nm with at least 500 mm in length is greater thanor equal to 85%, and combinations thereof. In some embodiments, theconcentration of Fe is <about 20 ppm.

In further embodiments, a glass article is provided comprising a glasssheet having between about 50 mol % to about 90 mol % SiO₂, betweenabout 0 mol % to about 15 mol % Al₂O₃, between about 0 mol % to about 12mol % B₂O₃, and about 2 mol % to about 25 mol % R_(x)O, wherein R is anyone or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba andx is 1, and wherein the glass produces 2 dB/500 mm or less of lightattenuation in the glass sheet.

In additional embodiments, a display device is provided comprising alight guide plate comprising a glass sheet having a Young's modulus ofbetween about 62 GPa to about 78 GPa, wherein the glass sheet comprisesbetween about 0 mol % to about 15 mol % Al₂O₃ and about 2 mol % to about25 mol % R_(x)O, wherein R is any one or more of Li, Na, K, Rb, Cs and xis 2, or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the transmittanceof the glass sheet at 450 nm with at least 500 mm in length is greaterthan or equal to 85%, the transmittance of the glass sheet at 550 nmwith at least 500 mm in length is greater than or equal to 90%, or thetransmittance of the glass sheet at 630 nm with at least 500 mm inlength is greater than or equal to 85%. In some embodiments, theconcentration of Fe of the glass sheet is <about 50 ppm, <about 20 ppmor <about 10 ppm. In some embodiments, the thickness of the displaydevice is less than 5 mm.

In further embodiments, a glass article is provided comprising a glasssheet having a Young's modulus of between about 62 GPa to about 78 GPa,wherein the glass sheet comprises between about 0 mol % to about 15 mol% Al₂O₃ and about 2 mol % to about 25 mol % R_(x)O, wherein R is any oneor more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba, and xis 1, and wherein the transmittance of the glass sheet at 450 nm with atleast 500 mm in length is greater than or equal to 85%, thetransmittance of the glass sheet at 550 nm with at least 500 mm inlength is greater than or equal to 90%, or the transmittance of theglass sheet at 630 nm with at least 500 mm in length is greater than orequal to 85%. In some embodiments, the concentration of Fe of the glasssheet is <about 50 ppm, <about 20 ppm, or <about 10 ppm. In someembodiments, the glass article is a light guide plate. In someembodiments, a display device can comprise the light guide platedescribed above wherein the light guide plate further comprises a glasssheet with a front face having a width and a height, a back faceopposite the front face, and a thickness between the front face and backface, forming four edges around the front and back faces, and whereinone or more edges of the light guide plate are illuminated by a lightsource.

In additional embodiments, a glass article is provided comprising aglass sheet having between about 0 mol % to about 15 mol % Al₂O₃, andabout 2 mol % to about 25 mol % R_(x)O, wherein R is any one or more ofLi, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1,wherein R_(x)O—Al₂O₃ is <25, and wherein the transmittance of the glasssheet at 450 nm with at least 500 mm in length is greater than or equalto 85%, the transmittance of the glass sheet at 550 nm with at least 500mm in length is greater than or equal to 90%, or the transmittance ofthe glass sheet at 630 nm with at least 500 mm in length is greater thanor equal to 85%. In some embodiments, the concentration of Fe of theglass sheet is <about 50 ppm, <about 20 ppm, or <about 10 ppm. In someembodiments, x=2 and R_(x)O—Al₂O₃<12; R_(x)O—Al₂O₃>0; R₂O—Al₂O₃<2; x=2and wherein R₂O—Al₂O₃—MgO>−15; and/or 0<(R_(x)O—Al₂O₃)<25,−11<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃—MgO)<11. In some embodiments,−1<(R₂O—Al₂O₃)<2 and −6<(R₂O—Al₂O₃—MgO)<1.

In further embodiments, a glass article is provided comprising a glasssheet having between about 50 mol % to about 90 mol % SiO₂, betweenabout 0 mol % to about 15 mol % Al₂O₃, between about 0 mol % to about 12mol % B₂O₃, and about 0 mol % to about 25 mol % R_(x)O, wherein R is anyone or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba andx is 1, wherein the glass produces 2 dB/500 mm or less of lightattenuation in the glass sheet, and wherein 0<(R_(x)O—Al₂O₃)<25,−11<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃—MgO)<11. In some embodiments, theconcentration of Fe of the glass sheet is <about 50 ppm. In someembodiments, Fe+30Cr+35Ni<about 60 ppm.

Additional features and advantages of the disclosure will be set forthin the detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the methods as described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present various embodiments of thedisclosure, and are intended to provide an overview or framework forunderstanding the nature and character of the claims. The accompanyingdrawings are included to provide a further understanding of thedisclosure, and are incorporated into and constitute a part of thisspecification. The drawings illustrate various embodiments of thedisclosure and together with the description serve to explain theprinciples and operations of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description can be further understood when readin conjunction with the following drawings.

FIG. 1 is a pictorial illustration of an exemplary embodiment of a lightguide plate;

FIG. 2 is a graph showing percentage light coupling versus distancebetween an LED and LGP edge;

FIG. 3 is a graph showing the estimated light leakage in dB/m versus RMSroughness of an LGP;

FIG. 4 is a graph showing an expected coupling (without Fresnel losses)as a function of distance between the LGP and LED for a 2 mm thick LED'scoupled into a 2 mm thick LGP;

FIG. 5 is a pictorial illustration of a coupling mechanism from an LEDto a glass LGP;

FIG. 6 is a graph showing an expected angular energy distributioncalculated from surface topology;

FIG. 7 is a pictorial illustration showing total internal reflection oflight at two adjacent edges of a glass LGP;

FIG. 8 is a cross sectional illustration of an exemplary LCD panel witha LGP in accordance with one or more embodiments;

FIG. 9 is a cross sectional illustration of an exemplary LCD panel witha LGP according to another embodiment;

FIG. 10 is a pictorial illustration showing an LGP with adhesion padsaccording to additional embodiments;

FIG. 11 is a graph showing attenuation for exemplary embodiments ofglass compositions; and

FIG. 12 is a graph showing transmission values for exemplary embodimentsof glass compositions.

DETAILED DESCRIPTION

Described herein are light guide plates, methods of making light guideplates and backlight units utilizing light guide plates in accordancewith embodiments of the present invention. Also described herein arearticles containing glass which can be used in display devices, inlighting applications and/or in architectural applications.

Current light guide plates used in LCD backlight applications aretypically made from PMMA material since this is one of the bestmaterials in term of optical transmission in the visible spectrum.However, PMMA presents mechanical problems that make large size (e.g.,50 inch diagonal and greater) displays challenging in term of mechanicaldesign, such as, rigidity, moisture absorption, and coefficient ofthermal expansion (CTE).

With regard to rigidity, conventional LCD panels are made of two piecesof thin glass (color filter substrate and TFT substrate) with a PMMAlight guide and a plurality of thin plastic films (diffusers, dualbrightness enhancement films (DBEF) films, etc.). Due to the poorelastic modulus of PMMA, the overall structure of the LCD panel does nothave sufficient rigidity, and additional mechanical structure isnecessary to provide stiffness for the LCD panel. It should be notedthat PMMA generally has a Young's modulus of about 2 GPa, while certainexemplary glasses have a Young's modulus ranging from about 60 GPa to 90GPa or more.

Regarding moisture absorption, humidity testing shows that PMMA issensitive to moisture and size can change by about 0.5%. For a PMMApanel having a length of one meter, this 0.5% change can increase thelength by 5 mm, which is significant and makes the mechanical design ofa corresponding backlight unit challenging. Conventional means to solvethis problem is leaving an air gap between the light emitting diodes(LEDs) and the PMMA light guide plate (LGP) to let the material expand.A problem with this approach is that light coupling is extremelysensitive to the distance from the LEDs to the LGP, which can cause thedisplay brightness to change as a function of humidity. FIG. 2 is agraph showing percentage light coupling versus distance between an LEDand LGP edge. With reference to FIG. 2, a relationship is shown whichillustrates the drawbacks of conventional measures to solve challengeswith PMMA. More specifically, FIG. 2 illustrates a plot of lightcoupling versus LED to LGP distance assuming both are 2 mm in height. Itcan be observed that the further the distance between LED and LGP, aless efficient light coupling is made between the LED and LGP. It shouldbe noted however, that while many embodiments are described hereinrelating to light guide plates and other display-related applications,the claims appended herewith should not be so limited as the glassarticles described herein can also find utility in lighting applicationsand in architectural applications.

With regard to CTE, the CTE of PMMA is about 75E-6 C⁻¹ and hasrelatively low thermal conductivity (0.2 W/m/K) while some glasses havea CTE of about 8E-6 C⁻¹ and a thermal conductivity of 0.8 W/m/K. Ofcourse, the CTE of other glasses can vary and such a disclosure shouldnot limit the scope of the claims appended herewith. PMMA also has atransition temperature of about 105° C., and when used an LGP, a PMMALGP material can become very hot whereby its low conductivity makes itdifficult to dissipate heat. Accordingly, using glass instead of PMMA asa material for light guide plates provides benefits in this regard, butconventional glass has a relatively poor transmission compared to PMMAdue mostly to iron and other impurities. Also some other parameters suchas surface roughness, waviness, and edge quality polishing can play asignificant role on how a glass light guide plate can perform. Accordingembodiments of the invention, glass light guide plates for use inbacklight units can have one or more of the following attributes.

Glass Light Guide Plate Structure and Composition

FIG. 1 is a pictorial illustration of an exemplary embodiment of a lightguide plate. With reference to FIG. 1, an illustration is provided of anexemplary embodiment having a shape and structure of an exemplary lightguide plate comprising a sheet of glass 100 having a first face 110,which may be a front face, and a second face opposite the first face,which may be a back face. The first and second faces may have a height,H, and a width, W. The first and/or second face(s) may have a roughnessthat is less than 0.6 nm, less than 0.5 nm, less than 0.4 nm, less than0.3 nm, less than 0.2 nm, less than 0.1 nm, or between about 0.1 nm andabout 0.6 nm.

The glass sheet may have a thickness, T, between the front face and theback face, where the thickness forms four edges. The thickness of theglass sheet may be less than the height and width of the front and backfaces. In various embodiments, the thickness of the plate may be lessthan 1.5% of the height of the front and/or back face. Alternatively,the thickness, T, may be less than about 3 mm, less than about 2 mm,less than about 1 mm, or between about 0.1 mm to about 3 mm. The height,width, and thickness of the light guide plate may be configured anddimensioned for use in an LCD backlight application.

A first edge 130 may be a light injection edge that receives lightprovided for example by a light emitting diode (LED). The lightinjection edge may scatter light within an angle less than 12.8 degreesfull width half maximum (FWHM) in transmission. The light injection edgemay be obtained by grinding the edge without polishing the lightinjection edge. The glass sheet may further comprise a second edge 140adjacent to the light injection edge and a third edge opposite thesecond edge and adjacent to the light injection edge, where the secondedge and/or the third edge scatter light within an angle of less than12.8 degrees FWHM in reflection. The second edge 140 and/or the thirdedge may have a diffusion angle in reflection that is below 6.4 degrees.It should be noted that while the embodiment depicted in FIG. 1 shows asingle edge 130 injected with light, the claimed subject matter shouldnot be so limited as any one or several of the edges of an exemplaryembodiment 100 can be injected with light. For example, in someembodiments, the first edge 130 and its opposing edge can both beinjected with light. Such an exemplary embodiment may be used in adisplay device having a large and or curvilinear width W. Additionalembodiments may inject light at the second edge 140 and its opposingedge rather than the first edge 130 and/or its opposing edge.Thicknesses of exemplary display devices can be less than about 10 mm,less than about 9 mm, less than about 8 mm, less than about 7 mm, lessthan about 6 mm, less than about 5 mm, less than about 4 mm, less thanabout 3 mm, or less than about 2 mm.

In various embodiments, the glass composition of the glass sheet maycomprise between 50-80 mol % SiO₂, between 0-20 mol % Al₂O₃, and between0-25 mol % B₂O₃, and less than 50 ppm iron (Fe) concentration. In someembodiments, there may be less than 25 ppm Fe, or in some embodimentsthe Fe concentration may be about 20 ppm or less. In variousembodiments, the thermal conduction of the light guide plate 100 may begreater than 0.5 W/m/K. In additional embodiments, the glass sheet maybe formed by a polished float glass, a fusion draw process, a slot drawprocess, a redraw process, or another suitable forming process.

According to one or more embodiments, the LGP can be made from a glasscomprising colorless oxide components selected from the glass formersSiO₂, Al₂O₃, and B₂O₃. The exemplary glass may also include fluxes toobtain favorable melting and forming attributes. Such fluxes includealkali oxides (Li₂O, Na₂O, K₂O, Rb₂O and Cs₂O) and alkaline earth oxides(MgO, CaO, SrO, ZnO and BaO). In one embodiment, the glass containsconstituents in the range of 50-80 mol % SiO₂, in the range of 0-20 mol% Al₂O₃, in the range of 0-25 mol % B₂O₃, and in the range of 5 and 20%alkali oxides, alkaline earth oxides, or combinations thereof.

In various embodiments, the mol % of Al₂O₃ may be in the range of about5% to about 22%, or alternatively in the range of about 10% to about22%, or in the range of about 18% to about 22%. In some embodiments, themol % of Al₂O₃ may be about 20%. In additional embodiments, the mol % ofAl₂O₃ may be between about 4% to about 10%, or between about 6% to about8%. In some embodiments, the mol % of Al₂O₃ may be about 7% to 8%.

In various embodiments, the mol % of B₂O₃ may be in the range of about0% to about 20%, or alternatively in the range of about 5% to about 15%,or in the range of about 5% to about 10%, in the range of about 6% toabout 8%. In some embodiments, the mol % of B₂O₃ may be about 5.5% ormay be about 7.5%

In various embodiments, the glass may comprise R_(x)O where R is Li, Na,K, Rb, Cs, and x is 2, or R is Zn, Mg, Ca, Sr or Ba, and x is 1, and themol % of R_(x)O can be approximately equal to the mol % of Al₂O₃.Alternatively, in various embodiments the Al₂O₃ mol % may be between upto 4 mol % greater than the R_(x)O and 4 mol % less than the R_(x)O. Insome embodiments, R_(x)O—Al₂O₃>0. In other embodiments,0<R_(x)O—Al₂O₃<25, <15 and all subranges therebetween. In furtherembodiments, x=2 and R₂O—Al₂O₃<25, <15 and all subranges therebetween.In additional embodiments, R₂O—Al₂O₃<2. In yet additional embodiments,x=2 and R₂O—Al₂O₃—MgO>−15 or >−10. In some embodiments,0<(R_(x)O—Al₂O₃)<25, −1<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃—MgO)<11. Infurther embodiments, −1<(R₂O—Al₂O₃)<2 and −6<(R₂O—Al₂O₃—MgO)<1.

These ratios play significant roles in establishing themanufacturability of the glass article as well as determining itstransmission performance. For example, glasses having R_(x)O—Al₂O₃approximately equal to or larger than zero will tend to have bettermelting quality but if R_(x)O—Al₂O₃ becomes too large of a value, thenthe transmission curve will be adversely affected. Similarly, ifR_(x)O—Al₂O₃ (e.g., R₂O—Al₂O₃) is within a given range (such as between−2 and 25 or between −2 and 15), then the glass will likely have hightransmission in the visible spectrum while maintaining meltability andsuppressing the liquidus temperature of a glass. Similarly,R₂O—Al₂O₃—MgO being approximately equal to or greater than zero willalso help suppress the liquidus temperature of the glass.

In one or more embodiments, the LGP glass can have low concentrations ofelements that produce visible absorption when in a glass matrix. Suchabsorbers include transition elements such as Ti, V, Cr, Mn, Fe, Co, Niand Cu, and rare earth elements with partially-filled f-orbitals,including Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er and Tm. Of these, the mostabundant in conventional raw materials used for glass melting are Fe, Crand Ni. Iron is a common contaminant in sand, the source of SiO₂, and isa typical contaminant as well in raw material sources for aluminum,magnesium and calcium. Chromium and nickel are typically present at lowconcentration in normal glass raw materials, but can be present invarious ores of sand and must be controlled at a low concentration.Additionally, chromium and nickel can be introduced via contact withstainless steel, e.g., when raw material or cullet is jaw-crushed,through erosion of steel-lined mixers or screw feeders, or unintendedcontact with structural steel in the melting unit itself. Theconcentration of iron in some embodiments can be specifically less than50 ppm, more specifically less than 40 ppm, or less than 25 ppm, and theconcentration of Ni and Cr can be specifically less than 5 ppm, and morespecifically less than 2 ppm. In further embodiments, the concentrationof all other absorbers listed above may be less than 1 ppm for each. Invarious embodiments the glass comprises 1 ppm or less of Co, Ni, and Cr,or alternatively less than 1 ppm of Co, Ni, and Cr. In variousembodiments, the transition elements (V, Cr, Mn, Fe, Co, Ni and Cu) maybe present in the glass at 0.1 wt % or less. In some embodiments, theconcentration of Fe can be <about 50 ppm, <about 40 ppm, <about 30 ppm,<about 20 ppm, or <about 10 ppm. In other embodiments,Fe+30Cr+35Ni<about 60 ppm, <about 50 ppm, <about 40 ppm, <about 30 ppm,<about 20 ppm, or <about 10 ppm.

Even in the case that the concentrations of transition metals are withinthe above described ranges, there can be matrix and redox effects thatresult in undesired absorption. As an example, it is well-known to thoseskilled in the art that iron occurs in two valences in glass, the +3 orferric state, and the +2 or ferrous state. In glass, Fe³⁺ producesabsorptions at approximately 380, 420 and 435 nm, whereas Fe²⁺ absorbsmostly at IR wavelengths. Therefore, according to one or moreembodiments, it may be desirable to force as much iron as possible intothe ferrous state to achieve high transmission at visible wavelengths.One non-limiting method to accomplish this is to add components to theglass batch that are reducing in nature. Such components could includecarbon, hydrocarbons, or reduced forms of certain metalloids, e.g.,silicon, boron or aluminum. However it is achieved, if iron levels werewithin the described range, according to one or more embodiments, atleast 10% of the iron in the ferrous state and more specifically greaterthan 20% of the iron in the ferrous state, improved transmissions can beproduced at short wavelengths. Thus, in various embodiments, theconcentration of iron in the glass produces less than 1.1 dB/500 mm ofattenuation in the glass sheet. Further, in various embodiments, theconcentration of V+Cr+Mn+Fe+Co+Ni+Cu produces 2 dB/500 mm or less oflight attenuation in the glass sheet when the ratio(Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O+MgO+ZnO+CaO+SrO+BaO)/Al₂O₃ for borosilicateglass is 4±0.5.

The valence and coordination state of iron in a glass matrix can also beaffected by the bulk composition of the glass. For example, iron redoxratio has been examined in molten glasses in the system SiO₂— K₂O—Al₂O₃equilibrated in air at high temperature. It was found that the fractionof iron as Fe³⁺ increases with the ratio K₂O/(K₂O+Al₂O₃), which inpractical terms will translate to greater absorption at shortwavelengths. In exploring this matrix effect, it was discovered that theratios (Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O)/Al₂O₃ and (MgO+CaO+ZnO+SrO+BaO)/Al₂O₃can also be important for maximizing transmission in borosilicateglasses. When this ratio is 1±0.2, transmission at short wavelengths canbe maximized for a given iron content. This is due in part to the higherproportion of Fe²⁺, and partially to matrix effects associated with thecoordination environment of iron.

Glass Roughness

FIG. 3 is a graph showing the estimated light leakage in dB/m versus RMSroughness of an LGP. With reference to FIG. 3, it can be shown thatsurface scattering plays a role in LGPs as light is bouncing many timeson the surfaces thereof. The curve depicted in FIG. 3 illustrates lightleakage in dB/m as a function of the RMS roughness of the LGP. FIG. 3shows that, to get below 1 dB/m, the surface quality needs to be betterthan about 0.6 nm RMS. This level of roughness can be achieved by eitherusing fusion draw process or float glass followed by polishing. Such amodel assumes that roughness acts like a Lambertian scattering surfacewhich means that we are only considering high spatial frequencyroughness. Therefore, roughness should be calculated by considering thepower spectral density and only take into account frequencies that arehigher than about 20 microns⁻¹.

UV Processing

In processing exemplary glass, ultraviolet (UV) light can also be used.For instance, light extraction features are often made by white printingdots on glass and UV is used to dry the ink. Also, extraction featurescan be made of a polymer layer with some specific structure on it andrequires UV exposure for polymerization. It has been discovered that UVexposure of glass can significantly affect transmission. According toone or more embodiments, a filter can be used during glass processing ofthe glass for an LGP to eliminate all wavelengths below about 400 nm.One possible filter consists in using the same glass as the one that iscurrently exposed.

Glass Waviness

Glass waviness is somewhat different from roughness in the sense that itis much lower frequency (in the mm or larger range). As such, wavinessdoes not contribute to extracting light since angles are very small butit modifies the efficiency of the extraction features since theefficiency is a function of the light guide thickness. Light extractionefficiency is, in general, inversely proportional to the waveguidethickness. Therefore, to keep high frequency image brightnessfluctuations below 5% (which is the human perception threshold thatresulted from our sparkle human perception analysis), the thickness ofthe glass needs to be constant within less than 5%. Exemplaryembodiments can have an A-side waviness of less than 0.3 um, less than0.2 um, less than 1 um, less than 0.08 um, or less than 0.06 um.

FIG. 4 is a graph showing an expected coupling (without Fresnel losses)as a function of distance between the LGP and LED for a 2 mm thick LED'scoupled into a 2 mm thick LGP. With reference to FIG. 4, light injectionin an exemplary embodiment usually involves placing the LGP in directproximity to one or more light emitting diodes (LEDs). According to oneor more embodiments, efficient coupling of light from an LED to the LGPinvolves using LED with a thickness or height that is less than or equalto the thickness of the glass. Thus, according to one or moreembodiments, the distance from the LED to the LGP can be controlled toimprove LED light injection. FIG. 4 shows the expected coupling (withoutFresnel losses) as a function of that distance and considering 2 mmheight LED's coupled into a 2 mm thick LGP. According to FIG. 4, thedistance should be <about 0.5 mm to keep coupling >about 80%. Whenplastic such as PMMA is used as a conventional LGP material, putting theLGP in physical contact with the LED's is somewhat problematic. First, aminimum distance is needed to let the material expand. Also LEDs tend toheat up significantly and, in case of physical contact, PMMA can getclose to its Tg (105° C. for PMMA). The temperature elevation that wasmeasured when putting PMMA in contact with LED's was about 50° C. closeby the LEDs. Thus for PMMA LGP, a minimum air gap is needed whichdegrades the coupling as shown in FIG. 4. According to embodiments ofthe subject matter in which glass LGPs are utilized, heating the glassis not a problem since Tg of glass is much higher and physical contactmay actually be an advantage since glass has a thermal conductioncoefficient that is large enough to make the LGP to be one additionalheat dissipation mechanism.

FIG. 5 is a pictorial illustration of a coupling mechanism from an LEDto a glass LGP. With reference to FIG. 5, assuming that the LED is closeto a lambertian emitter and assuming the glass index of refraction isabout 1.5, the angle α will stay smaller than 41.8 degrees (as in(1/1.5)) and the angle β will stay larger than 48.2 degrees (90−α).Since total internal reflection (TIR) angle is about 41.8 degrees, thismeans that all the light remains internal to the guide and coupling isclose to 100%. At the level of the LED injection, the injection face maycause some diffusion which will increase the angle at which light ispropagating into the LGP. In the event this angle becomes larger thanthe TIR angle, light may leak out of the LGP resulting in couplinglosses. However, the condition for not introducing significant losses isthat the angle in which light gets scattered should be less than48.2−41.8=+/−6.4 degrees (scattering angle<12.8 degrees). Thus,according to one or more embodiments, a plurality of the edges of theLGP may have a mirror polish to improve LED coupling and TIR. In someembodiments, three of the four edges have a mirror polish. Of course,these angles are exemplary only and should not limit the scope of theclaims appended herewith as exemplary scattering angles can be <20degrees, <19 degrees, <18 degrees, <17 degrees, <16 degrees, <14degrees, <13 degrees, <12 degrees, <11 degrees, or <10 degrees. Further,exemplary diffusion angles in reflection can be, but are not limited to,<15 degrees, <14 degrees, <13 degrees, <12 degrees, <11 degrees, <10degrees, <9 degrees, <8 degrees, <7 degrees, <6 degrees, <5 degrees, <4degrees, or <3 degrees.

FIG. 6 is a graph showing an expected angular energy distributioncalculated from surface topology. With reference to FIG. 6, the typicaltexture of a grinded only edge is illustrated where roughness amplitudeis relatively high (on the order of 1 nm) but special frequencies arerelatively low (on the order of 20 microns) resulting in a lowscattering angle. Further, this figure illustrates the expected angularenergy distribution calculated from the surface topology. As can beseen, scattering angle can be much less than 12.8 degrees full widthhalf maximum (FWHM).

In terms of surface definition, a surface can be characterized by alocal slope distribution e (x,y) that can be calculated, for instance,by taking the derivative of the surface profile. The angular deflectionin the glass can be calculated, in first approximation as:

θ′(x,y)θ=(x,y)/n

Therefore, the condition on the surface roughness is e (x,y)<n*6.4degrees with TIR at the 2 adjacent edges.

FIG. 7 is a pictorial illustration showing total internal reflection oflight at two adjacent edges of a glass LGP. With reference to FIG. 7,light injected into a first edge 130 can be incident on a second edge140 adjacent to the injection edge and a third edge 150 adjacent to theinjection edge, where the second edge 140 is opposite the third edge150. The second and third edges may also have a low roughness so thatthe incident light undergoes total internal reflectance (TIR) from thetwo edges adjacent the first edge. In the event light is diffused orpartially diffused at those interfaces, light may leak from each ofthose edges, thereby making the edges of an image appear darker. In someembodiments, light may be injected into the first edge 130 from an arrayof LED's 200 positioned along the first edge 130. The LED's may belocated a distance of less than 0.5 mm from the light injection edge.According to one or more embodiments, the LED's may have a thickness orheight that is less than or equal to the thickness of the glass sheet toprovide efficient light coupling to the light guide plate 100. Asdiscussed with reference to FIG. 1, FIG. 7 shows a single edge 130injected with light, but the claimed subject matter should not be solimited as any one or several of the edges of an exemplary embodiment100 can be injected with light. For example, in some embodiments, thefirst edge 130 and its opposing edge can both be injected with light.Additional embodiments may inject light at the second edge 140 and itsopposing edge 150 rather than the first edge 130 and/or its opposingedge. According to one or more embodiments, the two edges 140, 150 mayhave a diffusion angle in reflection that is below 6.4 degrees such thatthe condition on the roughness shape is represented by θ(x,y)<6.4/2=3.2degrees.

Color Shift Compensation

Although decreasing iron concentration can minimize absorption andyellow shift, it appears difficult to eliminate it completely. As anexample, at 32 ppm, a differential absorption coefficient of about 1dB/m between blue and red and green has been observed. This means that aone meter propagation (for a 60″ diagonal display) corresponds to adifferential loss of about 20%. The Δx, Δy in the measured for PMMA and32 ppm glass for a propagation distance of about 700 mm was for PMMA0.0021 and 0.0063 and for glass 0.0059 and 0.0163. To address residualcolor shift, several exemplary solutions may be implemented. In oneembodiment, light guide blue painting can be employed. By blue paintingthe light guide, one can artificially increase absorption in red andgreen and increase light extraction in blue. Accordingly, knowing howmuch differential color absorption exists, a blue paint pattern can beback calculated and applied that can compensate for color shift.

In one or more embodiments, shallow surface scattering features can beemployed to extract light with an efficiency that depends on thewavelength. As an example, a square grating has a maximum of efficiencywhen the optical path difference equals half of the wavelength.Accordingly, exemplary textures can be used to preferentially extractblue and can be added to the main light extraction texture. Inadditional embodiments, image processing can also be utilized. Forexample, an image filter can be applied that will attenuate blue closeto the edge where light gets injected. This may require shifting thecolor of the LEDs themselves to keep the right white color. In furtherembodiments, pixel geometry can be used to address color shift byadjusting the surface ratio of the RGB pixels in the panel andincreasing the surface of the blue pixels far away from the edge wherethe light gets injected.

LCD Panel Rigidity

One attribute of LCD panels is the overall thickness. In conventionalattempts to make thinner structures, lack of sufficient stiffness hasbecome a serious problem. Stiffness, however, can be increased with anexemplary glass LGP since the elastic modulus of glass is considerablylarger than that of PMMA. In some embodiments, to obtain a maximumbenefit from a stiffness point of view, all elements of the panel can bebonded together at the edge.

FIG. 8 is a cross sectional illustration of an exemplary LCD panel witha LGP in accordance with one or more embodiments. With reference to FIG.8, an exemplary embodiment of a panel structure 500 is provided. Thestructure comprises an LGP 100 mounted on a back plate 550 through whichlight can travel and be redirected toward the LCD or an observer. Astructural element 555 may affix the LGP 100 to the back plate 550, andcreate a gap between the back face of the LGP and a face of the backplate. A reflective and/or diffusing film 540 may be positioned betweenthe back face of the LGP 100 and the back plate 550 to send recycledlight back through the LGP 100. A plurality of LEDs, organic lightemitting diodes (OLEDs), or cold cathode fluorescent lamps (CCFLs) maybe positioned adjacent to the light injection edge 130 of the LGP, wherethe LEDs have the same width as the thickness of the LGP 100, and are atthe same height as the LGP 100. Conventional LCDs may employ LEDs orCCFLs packaged with color converting phosphors to produce white light.One or more backlight film(s) 570 may be positioned adjacent the frontface of the LGP 100. An LCD panel 580 may also be positioned above thefront face of the LGP 100 with a structural element 585, and thebacklight film(s) 570 may be located in the gap between the LGP 100 andLCD panel 580. Light from the LGP 100 can then pass through the film570, which can backscatter high angle light and reflect low angle lightback toward the reflector film 540 for recycling and may serve toconcentrate light in the forward direction (e.g., toward the user). Abezel 520 or other structural member may hold the layers of the assemblyin place. A liquid crystal layer (not shown) may be used and maycomprise an electro-optic material, the structure of which rotates uponapplication of an electric field, causing a polarization rotation of anylight passing through it. Other optical components can include, e.g.,prism films, polarizers, or TFT arrays, to name a few. According tovarious embodiments, the angular light filters disclosed herein can bepaired with a transparent light guide plate in a transparent displaydevice. In some embodiments, the LGP can be bonded to the structure(using optically clear adhesive OCA or pressure sensitive adhesive PSA)where the LGP is placed in optical contact with some of the structuralelements of the panel. In other words, some of the light may leak out ofthe light guide through the adhesive. This leaked light can becomescattered or absorbed by those structural elements. As explained above,the first edge where the LEDs are coupled into the LGP and the twoadjacent edges where the light needs to be reflected in TIR can avoidthis problem if properly prepared.

Exemplary widths and heights of the LGP generally depend upon the sizeof the respective LCD panel. It should be noted that embodiments of thepresent subject matter are applicable to any size LCD panel whethersmall (<40″ diagonal) or large (>40″ diagonal) displays.

FIG. 9 is a cross sectional illustration of an exemplary LCD panel witha LGP according to another embodiment. With reference to FIG. 9,additional embodiments can utilize a reflective layer. Losses in someembodiments can be minimized by inserting a reflective surface betweenthe LGP and the epoxy by either metalizing the glass with, for instance,silver or inkjet print with reflective ink. In other embodiments, highlyreflective films (such as Enhanced Specular Reflector films (made by3M)) may be laminated with the LGP.

FIG. 10 is a pictorial illustration showing an LGP with adhesion padsaccording to additional embodiments. With reference to FIG. 10, adhesionpads instead of a continuous adhesive can be used in which the pads 600are shown as a series of dark squares. Thus, to limit the surface of LGPthat is optically connected to the structural elements, the illustratedembodiment can employ 5×5 mm square pads every 50 mm to providesufficient adhesion where extracted light is less than 4%. Of course,the pads 600 may be circular or another polygon in form and may beprovided in any array or spacing and such a description should not limitthe scope of the claims appended herewith.

Glass Composition

Further to the exemplary compositions about, in additional exemplaryglass compositions, the ratio of Al₂O₃—R_(x)O was varied. For example,glasses with Al₂O₃ greater than Na₂O by 4 mol %, glasses with Al₂O₃equal to Na₂O, and glasses with Al₂O₃ less than Na₂O by −4 mol % wereprepared for the following compositions shown in Table 1 below.

TABLE 1 Al₂O₃ − Al₂O₃ − Na₂O = 4 Al₂O₃ − Na₂O = 0 Na₂O = −4 SiO2 59.959.9 59.9 Al2O3 22 20 18 Na2O 18 20 22 transition 0.1 0.1 0.1 element(wt %) tramp Fe (ppm) 20 20 20

FIG. 11 is a graph showing attenuation for exemplary embodiments ofglass compositions. With reference to FIG. 11, the figure illustratesabsorption (dB/500 mm/ppm) for glass compositions with Al₂O₃—R_(x)O=4,Al₂O₃—R_(x)O=0, and Al₂O₃—R_(x)O=−4 and where R is Li, Na, K, Rb, Cs,Mg, Ca, Sr or Ba and x is 1 or 2. Similar results were obtained when Ris an alkali cation (Li, Na, K, Rb or Cs) and when R is an alkalineearth cation (Mg, Ca, Sr, Ba) as these cations completely lose theirvalence electrons to oxygen and therefore cannot directly affect eitherthe oxidation state or the coordination environment of the transitionmetals. When the glass has Al₂O₃>R_(x)O there is a low absorption atlong wavelengths but a rapidly rising attenuation at short wavelengths,whereas a glass with Al₂O₃<R_(x)O has low attenuation at shortwavelengths and high attenuation at long wavelengths. In comparison, aglass with Al₂O₃˜_(x)O shows low attenuation throughout the wavelengthrange. A higher absorption at some wavelengths than at others can causea “color shift” to the white light launched from the edge of the LGP.Therefore it follows that a glass with Al₂O₃>R_(x)O attenuates morestrongly at blue wavelengths and therefore would cause a color shift ofthe white light toward green wavelengths.

The attenuation impact of each element may be estimated by identifyingthe wavelength in the visible where it attenuates most strongly. Inexamples shown in Table 2 below, the coefficients of absorption of thevarious transition metals have been experimentally determined inrelation to the concentrations of Al₂O₃ to R_(x)O (however, only themodifier Na₂O has been shown below for brevity).

TABLE 2 dB/ppm/500 mm Al₂O₃ > Na₂O Al₂O₃ = Na₂O Al₂O₃ < Na₂O V 0.1190.109 0.054 Cr 2.059 1.869 9.427 Mn 0.145 0.06 0.331 Fe 0.336 0.0370.064 Co 1.202 2.412 3.7 Ni 0.863 0.617 0.949 Cu 0.108 0.092 0.11

With the exception of V (vanadium), a minimum attenuation is found forglasses with concentrations of Al₂O₃=Na₂O, or more generally forAl₂O₃˜R_(x)O. In various instances the transition metals may assume twoor more valences (e.g., Fe can be both +2 and +3), so to some extent theredox ratio of these various valences may be impacted by the bulkcomposition. Transition metals respond differently to what are known as“crystal field” or “ligand field” effects that arise from interactionsof the electrons in their partially-filled d-orbital with thesurrounding anions (oxygen, in this case), particularly if there arechanges in the number of anion nearest neighbors (also referred to ascoordination number). Thus, it is likely that both redox ratio andcrystal field effects contribute to this result.

The coefficients of absorption of the various transition metals may alsobe utilized to determine the attenuation of the glass composition over apath length in the visible spectrum (i.e., between 380 and 700 nm), asshown in Table 3 below.

TABLE 3 Al₂O₃ − R_(x)O = 4 0.119V + 2.059Cr + 0.145Mn + 0.336Fe +1.202Co + 0.863Ni + 0.108Cu < 2 Al₂O₃ ~ R_(x)O = 0 0.109V + 1.869Cr +0.06Mn + 0.037Fe + 2.412Co + 0.617Ni + 0.092Cu < 2 Al₂O₃ < R_(x)O = −40.054V + 9.427Cr + 0.331Mn + 0.064Fe + 3.7Co + 0.949Ni + 0.11Cu < 2

Of course the values identified in Table 3 are exemplary only should notlimit the scope of the claims appended herewith. For example, it wasalso unexpectedly discovered that a high transmittance glass could beobtained when Fe+30Cr+35Ni<60 ppm. In some embodiments, theconcentration of Fe can be <about 50 ppm, <about 40 ppm, <about 30 ppm,<about 20 ppm, or <about 10 ppm. In other embodiments,Fe+30Cr+35Ni<about 50 ppm, <about 40 ppm, <about 30 ppm, <about 20 ppm,or <about 10 ppm.

Tables 4 and 5 provide some exemplary non-limiting examples of glassesprepared for embodiments of the present subject matter.

TABLE 4 wt % mol % SiO₂ (diff) 58.58 64.66 Al₂O₃ 21.36 13.89 B₂O₃ 5.35.05 Na₂O 12.95 13.86 K₂O 0.01 0.01 MgO 1.52 2.5 CaO 0.03 0.04 Al₂O₃ −R_(x)O −2.52 Fe (ppm) 20

TABLE 5 mol % SiO₂ (diff) 72.22 Al₂O₃ 7.62 B₂O₃ 7.58 Na₂O 8.08 SrO 2.1MgO 2.25 K₂O CaO Al₂O₃ − R_(x)O −4.81 Fe (ppm) <20 ppm

All other transition metals were below detection limits. In thenon-limiting examples, the value of Al₂O₃— R_(x)O indicates thatmodifiers are in excess of aluminum, so using the table above, thepredicted attenuation is roughly 60% of the way between the glassesabove with Al₂O₃—R_(x)O=0 and Al₂O₃—R_(x)O=−4:20 ppm Fe×[0.6*0.067dB/ppm/500 mm+0.4×0.037 dB/ppm/500 mm]=1.06 dB/500 mm path length. Thisgenerally corresponds to about 78% internal transmission or more.

In some embodiments, the glass may comprise about 50 wt % to about 60 wt% SiO₂, about 15 wt % to about 22 wt % Al₂O₃, about 15 wt % to about 22wt % R_(x)O, about 0 wt % to about 6 wt % of B₂O₃, and less than 50 ppmof Fe, with the proviso that the wt % of SiO₂ makes up the balance ofthe composition after determining the wt % of Al₂O₃, B₂O₃, R_(x)O, ppmof Fe, and the concentration of any other residual components (e.g.,SO₃), which is less than 0.1 wt %. In some embodiments, the mol % ofAl₂O₃ is approximately equal to mol % of R_(x)O where R is Li, Na, K,Rb, Cs, and x is 2, or R is Mg, Zn, Ca, Sr or Ba, and x is 1. In someembodiments, the composition comprises 50 ppm or less of Fe, 40 ppm orless of Fe, 30 ppm or less of Fe, 20 ppm or less of Fe, 10 ppm or lessof Fe, or 5 ppm or less of Fe.

In additional embodiments, the glass may comprise about 50 mol % toabout 90 mol % SiO₂, from about 65 mol % to about 75 mol % SiO₂, or fromabout 65 mol % to about 72 mol % SiO₂ and all subranges therebetween.The glass may also comprise from about 0 mol % to about 15 mol % Al₂O₃,or from about 5 mol % to about 13 mol % Al₂O₃ and all subrangestherebetween. The glass may further comprise from about 0 mol % to about12 mol % B₂O₃, or from about 5 mol % to about 8 mol % B₂O₃ and allsubranges therebetween. The glass may further comprise from about 2 mol% to about 25 mol % R_(x)O, from about 2 mol % to about 19 mol % R_(x)O,from about 5 mol % to about 15 mol % R_(x)O, from about 10 mol % toabout 16 mol % R_(x)O, or from about 11 mol % to about 16 mol % R_(x)Oand all subranges therebetween. In such embodiments, there should beless than 50 ppm of Fe or less than 20 ppm Fe and/or the concentrationof any other residual components (e.g., SO₃, V, Ni, etc.) should be lessthan 0.5 mol %. In some embodiments, the mol % of Al₂O₃ is approximatelyequal to the mol % of R_(x)O where R is Li, Na, K, Rb, Cs, and x is 2,or R is Mg, Ca, Zn, Sr or Ba, and x is 1.

Exemplary compositions as heretofore described can thus be used toachieve a strain point ranging from about 525° C. to about 575° C., fromabout 540° C. to about 560° C., or from about 545° C. to about 555° C.and all subranges therebetween. In one embodiment, the strain point isabout 551° C. An exemplary annealing point can range from about 575° C.to about 605° C., from about 590° C. to about 600° C., or from about595° C. to about 600° C. and all subranges therebetween. In oneembodiment, the annealing point is about 596° C. An exemplary softeningpoint of a glass ranges from about 800° C. to about 860° C., from about820° C. to about 840° C., or from about 825° C. to about 835° C. and allsubranges therebetween. In one embodiment, the strain point is about834° C. The density of exemplary glass compositions can range from about1.95 gm/cc @ 20 C to about 2.7 gm/cc @ 20 C, from about 2.1 gm/cc @ 20 Cto about 2.4 gm/cc @ 20 C, or from about 2.2 gm/cc @ 20 C to about 2.4gm/cc @ 20 C and all subranges therebetween. In one embodiment thedensity is about 2.38 gm/cc @ 20 C. The Young's modulus of exemplaryembodiments can range from about 62 GPa to about 90 GPa, from about 65GPa to about 75 GPa, or from about 68 GPa to about 72 GPa and allsubranges therebetween. In one embodiment, the Young's modulus is about69.2 GPa. The shear modulus of exemplary embodiments can range fromabout 22 GPa to about 35 GPa, from about 25 GPa to about 32 GPa, or fromabout 28 GPa to about 30 GPa and all subranges therebetween. In oneembodiment, the shear modulus is about 28.7 GPa. CTEs (0-300° C.) forexemplary embodiments can range from about 30×10-7/° C. to about95×10-7/° C., from about 50×10-7/° C. to about 70×10-7/° C., or fromabout 55×10-7/° C. to about 65×10-7/° C. and all subranges therebetween.In one embodiment the CTE is about 55.4×10-7/° C. Additional embodimentscan include a Poisson's ratio from about 0.1 to about 0.3, from about0.15 to about 0.25, from about 0.19 to about 0.21 and all subrangestherebetween. In one embodiment, an exemplary Poisson's ratio is about0.206.

FIG. 12 is a graph showing transmission values for exemplary embodimentsof glass composition. With reference to FIG. 12, the minimum intransmission from 400-700 nm should be about 77%, which is close to thevalue calculated with the coefficients. In the particular sample, theexperimental glasses contained only sodium, whereas other productionglass may contain sodium, magnesium, calcium, barium, strontium, zincand potassium. The different contributing alkali or alkaline earthoxides may be summed together to calculate a total R_(x)O, such that themodifier may be any of the alkali or alkaline earth oxides. Furthermore,the attenuation that is obtained is unaffected by the SiO₂ and B₂O₃, asdemonstrated in this example, and thus their relative proportions do notdirectly affect the result. While not shown in FIG. 12, certainembodiments and compositions described in the previous paragraphs haveprovided a transmission from 400-700 nm greater than 90%, greater than91%, greater than 92%, greater than 93%, greater than 94%, and evengreater than 95%. Thus, exemplary embodiments described herein can havea transmittance at 450 nm with 500 mm in length of greater than 85%,greater than 90%, greater than 91%, greater than 92%, greater than 93%,greater than 94%, and even greater than 95%. Exemplary embodimentsdescribed herein can also have a transmittance at 550 nm with 500 mm inlength of greater than 90%, greater than 91%, greater than 92%, greaterthan 93%, greater than 94%, and even greater than 96%. Furtherembodiments described herein can have a transmittance at 630 nm with 500mm in length of greater than 85%, greater than 90%, greater than 91%,greater than 92%, greater than 93%, greater than 94%, and even greaterthan 95%.

The various embodiments, therefore relate to a silicate or borosilicateglass compromising Al₂O₃ and further comprising modifier oxides selectedfrom the list Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O, MgO, ZnO, CaO, SrO, BaO, suchthat −4<=Al₂O₃—R_(x)O<=4, and the total concentration of all transitionmetals in ppm satisfies an appropriately weighted sums of the formulaspresented in in Table 2 above.

As a further example, a glass satisfying these constraints may show anattenuation between 380 nm and 700 nm of no more than 2 dB (about 63%minimum transmission) over a path length of 500 mm. For LGPs withdimensions less than 500 mm, for example in smaller devices, such as thedisplays in notebook computers, the shorter path length can result in agreater transmission (e.g., for a 250 mm path (9.8″), the attenuationwould be 1 dB). Principles and embodiments of the present subject matteralso relate to sheets of optical quality glass prepare by a fusiondraw-down process for light guide plates.

One or more embodiments relate to glass sheets having a width of atleast about 1143 mm (45 inches) and a thickness of between 2 mm and 8mm, with an attenuation of less than 4 dB for light wavelengths betweenabout 380 nm and about 700 nm. Using wt %, the glass may be high silicacontent glasses having a composition of between about 80 wt % and 95 wt% SiO₂, and between about 14 wt % and 4 wt % B₂O₃, between about 2 wt %and 4 wt % Na₂O, with a balance comprising Al₂O₃ and/or K₂O. In variousembodiments, the SiO₂, B₂O₃, Na₂O, Al₂O₃, and K₂O, components are allessentially free of iron (Fe) (i.e., less than 20 ppm Fe (20 mg. Fe/kg.of glass)), and particularly free of iron in a +3 oxidation state (Fe³⁺)(i.e., the Fe includes less than about 80% Fe as Fe³⁺. In variousembodiments, the glass has a composition consisting essentially ofbetween about 4 wt % and 14 wt % B₂O₃, between about 2 wt % and 4% Na₂O,between about 2 wt % and 4% Al₂O₃ and/or K₂O, and the balance SiO₂,where each of the components is essentially iron free (i.e., less than20 ppm Fe (20 mg. Fe/kg. of glass)).

Embodiments that consist essentially of SiO₂, B₂O₃, Na₂O, and K₂O,exclude Al₂O₃, Li₂O, Rb₂O, Cs₂O, MgO, CaO, SrO, ZnO, and BaO, andincludes essentially no Fe, Ni, Co, or Cr (i.e., less than 20 ppm Fe,Ni, Co, or Cr, as the oxide). Essentially free also indicates that noneof the Fe, Ni, Co, or Cr that may be present was intentionally added tothe glass composition. In various embodiments, the Fe includes less than10 ppm Fe as Fe³⁺. The ferric iron (Fe³⁺) is minimized while the ferrousiron (Fe²⁺) is maximized to reduce the absorption in the UV/blue regionof the visible spectrum, which may otherwise produce a yellow tint.

In various embodiments, cerium oxide (CeO₂) may be excluded from theglass composition to reduce the amount of Fe³⁺. In one or moreembodiments, the base glass materials (e.g., SiO₂, B₂O₃, Na₂O, Al₂O₃,and K₂O) are all of high purity and essentially free of Fe, Ni, Co, andCr. Using wt %, one or more embodiments consists essentially of at least81 wt % SiO₂, at least 10 wt % B₂O₃, at least 2 wt % Na₂O, and at least2 wt % K₂O with the proviso that neither the Na₂O nor the K₂O makes upmore than 4 wt % of the total glass composition. One or more embodimentsconsist essentially of about 80 wt % SiO₂, about 14 wt % B₂O₃, about 4wt % Na₂O, and about 2 wt % K₂O, with essentially no Fe, Ni, Co, or Cr.In various embodiments the glass comprises 2 ppm or less of Co, Ni, andCr, or 1 ppm or less of Co, Ni, and Cr, or less than 1 ppm of Co, Ni,and Cr. In various embodiments, the concentration ofV+Cr+Mn+Fe+Co+Ni+Cu<20 ppm. One or more embodiments relate to lightguide plate having a composition consisting essentially of SiO₂, B₂O₃,Na₂O, Al₂O₃, and K₂O, wherein the glass sheet has a width of at least1143 mm (45 in.) and a thickness of between 2 mm and 8 mm, and atransmission of at least 80% across the width of the LGP.

In one or more embodiments, the LGP has a width of at least about 1270mm and a thickness of between about 0.5 mm and about 3.0 mm, wherein thetransmittance of the LGP is at least 80% per 500 mm. In variousembodiments, the thickness of the LGP is between about 1 mm and about 8mm, and the width of the plate is between about 1100 mm and about 1300mm.

In one or more embodiments, the LGP can be strengthened. For example,certain characteristics, such as a moderate compressive stress (CS),high depth of compressive layer (DOL), and/or moderate central tension(CT) can be provided in an exemplary glass sheet used for a LGP. Oneexemplary process includes chemically strengthening the glass bypreparing a glass sheet capable of ion exchange. The glass sheet canthen be subjected to an ion exchange process, and thereafter the glasssheet can be subjected to an anneal process if necessary. Of course, ifthe CS and DOL of the glass sheet are desired at the levels resultingfrom the ion exchange step, then no annealing step is required. In otherembodiments, an acid etching process can be used to increase the CS onappropriate glass surfaces. The ion exchange process can involvesubjecting the glass sheet to a molten salt bath including KNO₃,preferably relatively pure KNO₃ for one or more first temperatureswithin the range of about 400-500° C. and/or for a first time periodwithin the range of about 1-24 hours, such as, but not limited to, about8 hours. It is noted that other salt bath compositions are possible andwould be within the skill level of an artisan to consider suchalternatives. Thus, the disclosure of KNO₃ should not limit the scope ofthe claims appended herewith. Such an exemplary ion exchange process canproduce an initial CS at the surface of the glass sheet, an initial DOLinto the glass sheet, and an initial CT within the glass sheet.Annealing can then produce a final CS, final DOL and final CT asdesired.

Some embodiments comprise a glass article, comprising a glass sheet witha front face having a width and a height, a back face opposite the frontface, and a thickness between the front face and back face, forming fouredges around the front and back faces, wherein the glass sheet comprisesbetween about 50 mol % to about 90 mol % SiO₂, between about 0 mol % toabout 20 mol % Al₂O₃, 0 mol % to about 20 mol % B₂O₃, and about 0 mol %to about 25 mol % R_(x)O, wherein R is any one or more of Li, Na, K, Rb,Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the glassproduces less than or equal to 2 dB/500 mm absorption. In furtherembodiments, R_(x)O—Al₂O₃>0; 0<R_(x)O—Al₂O₃<15; x=2 and R₂O—Al₂O₃<15;R₂O—Al₂O₃<2; x=2 and R₂O—Al₂O₃—MgO>−15; 0<(R_(x)O—Al₂O₃)<25,−11<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃—MgO)<11; and/or −1<(R₂O—Al₂O₃)<2and −6<(R₂O—Al₂O₃—MgO)<1. In other embodiments, the glass article is alight guide plate. In some embodiments, a roughness of at least one faceis less than 0.6 nm. In additional embodiments, the thickness of theplate is between about 0.5 mm and about 8 mm. In further embodiments,the thickness has a variation of less than 5%. In some embodiments, thelight guide plate is manufactured from a fusion draw process, slot drawprocess, or a float process. In further embodiments, at least 10% of theiron is Fe²⁺. In some embodiments, the glass article has a liquidusviscosity greater than 100 kP and a T_(200P) temperature below 1760° C.In some embodiments, the glass comprises less than 1 ppm each of Co, Ni,and Cr. In some embodiments, the concentration of Fe is <about 50 ppm,<about 20 ppm, or <about 10 ppm. In other embodiments,Fe+30Cr+35Ni<about 60 ppm, Fe+30Cr+35Ni<about 40 ppm, Fe+30Cr+35Ni<about20 ppm, or Fe+30Cr+35Ni<about 10 ppm. In some embodiments, at least oneedge is a light injection edge (polished or unpolished) that scatterslight within an angle less than 12.8 degrees full width half maximum(FWHM) in transmission. In some embodiments, the glass sheet furthercomprises a second edge adjacent to the light injection edge and a thirdedge opposite the second edge and adjacent to the light injection edge,wherein the second edge and the third edge scatter light within an angleof less than 12.8 degrees FWHM in reflection. The second edge and thethird edge can have a diffusion angle in reflection that is below 6.4degrees. In some embodiments, the transmittance at 450 nm with at least500 mm in length is greater than or equal to 85%, the transmittance at550 nm with at least 500 mm in length is greater than or equal to 90%,or the transmittance at 630 nm with at least 500 mm in length is greaterthan or equal to 85%, and combinations thereof. In some embodiments, thedensity is between about 1.95 gm/cc @ 20 C to about 2.7 gm/cc @ 20 C,the Young's modulus is between about 62 GPa to about 90 GPa, and/or theCTE (0-300° C.) is between about 30×10-7/° C. to about 95×10-7/° C. Insome embodiments, the glass sheet is chemically strengthened. In someembodiments, T_(200P) temperature is below 1760° C., below 1730° C. orbelow 1700° C. In some embodiments, a liquidus viscosity can be greaterthan 100 kP or greater than 500 kP.

In additional embodiments, a glass article is provided comprising aglass sheet with a front face having a width and a height, a back faceopposite the front face, and a thickness between the front face and backface, forming four edges around the front and back faces, wherein theglass sheet comprises between about 60 mol % to about 80 mol % SiO₂,between about 0.1 mol % to about 15 mol % Al₂O₃, 0 mol % to about 12 mol% B₂O₃, and about 0.1 mol % to about 15 mol % R2O and about 0.1 mol % toabout 15 mol % RO, wherein R is any one or more of Li, Na, K, Rb, Cs andx is 2, or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the glassproduces less than or equal to 2 dB/500 mm absorption. In someembodiments, Fe+30Cr+35Ni<about 60 ppm, Fe+30Cr+35Ni<about 40 ppm,Fe+30Cr+35Ni<about 30 ppm, or Fe+30Cr+35Ni<about 20 ppm. In someembodiments, 0<(R_(x)O—Al₂O₃)<25, −11<(R₂O—Al₂O₃)<11, and−15<(R₂O—Al₂O₃—MgO)<11. In some embodiments, the glass produces lessthan or equal to 0.5 dB/500 mm absorption or less than or equal to 0.25dB/500 mm absorption.

In further embodiments, a glass article is provided comprising a glasssheet having between about 50 mol % to about 90 mol % SiO₂, betweenabout 0 mol % to about 15 mol % Al₂O₃, between about 0 mol % to about 12mol % B₂O₃, and about 2 mol % to about 25 mol % R_(x)O, wherein R is anyone or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba andx is 1, and wherein Fe+30Cr+35Ni<about 60 ppm.

In additional embodiments, a light guide plate is provided comprising aglass sheet having between about 0 mol % to about 15 mol % Al₂O₃, andabout 0 mol % to about 25 mol % R_(x)O, wherein R is any one or more ofLi, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1, andwherein Fe is <about 50 ppm. In some embodiments, the light guide platefurther comprises between about 50 mol % to about 90 mol % SiO₂ andbetween about 0 mol % to about 12 mol % B₂O₃. In some embodiments, theglass comprises less than 1 ppm of each of Co, Ni, and Cr. In someembodiments, the glass produces less than or equal to 2 dB/500 mm oflight attenuation, less than or equal to 1 dB/500 mm absorption, or lessthan or equal to 0.5 dB/500 mm absorption. In other embodiments,Fe+30Cr+35Ni<about 60 ppm or Fe+30Cr+35Ni<about 20 ppm. In someembodiments, the mol % of Al₂O₃ is <or substantially equal to the mol %R_(x)O; R_(x)O—Al₂O₃>0; 0<R_(x)O—Al₂O₃<25; x=2 and R₂O—Al₂O₃<15;R₂O—Al₂O₃<2; x=2 and R₂O—Al₂O₃—MgO>−15. In some embodiments,0<(R_(x)O—Al₂O₃)<25, −11<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃—MgO)<11. Insome embodiments, −1<(R₂O—Al₂O₃)<2 and −6<(R₂O—Al₂O₃—MgO)<1. In someembodiments, the transmittance at 450 nm with at least 500 mm in lengthis greater than or equal to 85%, the transmittance at 550 nm with atleast 500 mm in length is greater than or equal to 90%, or thetransmittance at 630 nm with at least 500 mm in length is greater thanor equal to 85%, and combinations thereof. In some embodiments, theconcentration of Fe is <about 20 ppm or the concentration of Fe is<about 10 ppm. In some embodiments, the glass sheet is chemicallystrengthened. In further embodiments, a display device comprises thelight guide plate described above wherein the light guide plate furthercomprises a glass sheet with a front face having a width and a height, aback face opposite the front face, and a thickness between the frontface and back face, forming four edges around the front and back faces,and wherein one or more edges of the light guide plate are illuminatedby a light source. The light source can be selected from the groupconsisting of an LED, CCFL, OLED, and combinations thereof. The displaydevice can have glass comprising less than 1 ppm of each of Co, Ni, andCr. This glass can produce less than or equal to 2 dB/500 mm of lightattenuation. In some embodiments, Fe+30Cr+35Ni<about 60 ppm and/or themol % of Al₂O₃ is <or substantially equal to the mol % R_(x)O. In someembodiments, the thickness of the display device is less than 5 mm. Insome embodiments, the transmittance at 450 nm with at least 500 mm inlength is greater than or equal to 85%, the transmittance at 550 nm withat least 500 mm in length is greater than or equal to 90%, or thetransmittance at 630 nm with at least 500 mm in length is greater thanor equal to 85%, and combinations thereof. In some embodiments, theconcentration of Fe is <about 20 ppm.

In further embodiments, a glass article is provided comprising a glasssheet having between about 50 mol % to about 90 mol % SiO₂, betweenabout 0 mol % to about 15 mol % Al₂O₃, between about 0 mol % to about 12mol % B₂O₃, and about 2 mol % to about 25 mol % R_(x)O, wherein R is anyone or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba andx is 1, and wherein the glass produces 2 dB/500 mm or less of lightattenuation in the glass sheet.

In additional embodiments, a display device is provided comprising alight guide plate comprising a glass sheet having a Young's modulus ofbetween about 62 GPa to about 78 GPa, wherein the glass sheet comprisesbetween about 0 mol % to about 15 mol % Al₂O₃ and about 2 mol % to about25 mol % R_(x)O, wherein R is any one or more of Li, Na, K, Rb, Cs and xis 2, or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the transmittanceof the glass sheet at 450 nm with at least 500 mm in length is greaterthan or equal to 85%, the transmittance of the glass sheet at 550 nmwith at least 500 mm in length is greater than or equal to 90%, or thetransmittance of the glass sheet at 630 nm with at least 500 mm inlength is greater than or equal to 85%. In some embodiments, theconcentration of Fe of the glass sheet is <about 50 ppm, <about 20 ppmor <about 10 ppm. In some embodiments, the thickness of the displaydevice is less than 5 mm.

In further embodiments, a glass article is provided comprising a glasssheet having a Young's modulus of between about 62 GPa to about 78 GPa,wherein the glass sheet comprises between about 0 mol % to about 15 mol% Al₂O₃ and about 2 mol % to about 25 mol % R_(x)O, wherein R is any oneor more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba, and xis 1, and wherein the transmittance of the glass sheet at 450 nm with atleast 500 mm in length is greater than or equal to 85%, thetransmittance of the glass sheet at 550 nm with at least 500 mm inlength is greater than or equal to 90%, or the transmittance of theglass sheet at 630 nm with at least 500 mm in length is greater than orequal to 85%. In some embodiments, the concentration of Fe of the glasssheet is <about 50 ppm, <about 20 ppm, or <about 10 ppm. In someembodiments, the glass article is a light guide plate. In someembodiments, a display device can comprise the light guide platedescribed above wherein the light guide plate further comprises a glasssheet with a front face having a width and a height, a back faceopposite the front face, and a thickness between the front face and backface, forming four edges around the front and back faces, and whereinone or more edges of the light guide plate are illuminated by a lightsource.

In additional embodiments, a glass article is provided comprising aglass sheet having between about 0 mol % to about 15 mol % Al₂O₃, andabout 2 mol % to about 25 mol % R_(x)O, wherein R is any one or more ofLi, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1,wherein R_(x)O—Al₂O₃ is <25, and wherein the transmittance of the glasssheet at 450 nm with at least 500 mm in length is greater than or equalto 85%, the transmittance of the glass sheet at 550 nm with at least 500mm in length is greater than or equal to 90%, or the transmittance ofthe glass sheet at 630 nm with at least 500 mm in length is greater thanor equal to 85%. In some embodiments, the concentration of Fe of theglass sheet is <about 50 ppm, <about 20 ppm, or <about 10 ppm. In someembodiments, x=2 and R_(x)O—Al₂O₃<12; R_(x)O—Al₂O₃>0; R₂O—Al₂O₃<2; x=2and wherein R₂O—Al₂O₃—MgO>−15; and/or 0<(R_(x)O—Al₂O₃)<25,−11<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃MgO)<11. In some embodiments,−1<(R₂O—Al₂O₃)<2 and −6<(R₂O—Al₂O₃—MgO)<1.

In further embodiments, a glass article is provided comprising a glasssheet having between about 50 mol % to about 90 mol % SiO₂, betweenabout 0 mol % to about 15 mol % Al₂O₃, between about 0 mol % to about 12mol % B₂O₃, and about 0 mol % to about 25 mol % R_(x)O, wherein R is anyone or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba andx is 1, wherein the glass produces 2 dB/500 mm or less of lightattenuation in the glass sheet, and wherein 0<(R_(x)O—Al₂O₃)<25,−11<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃—MgO)<11. In some embodiments, theconcentration of Fe of the glass sheet is <about 50 ppm. In someembodiments, Fe+30Cr+35Ni<about 60 ppm.

Some embodiments provide a glass article, comprising a glass sheet witha front face having a width and a height, a back face opposite the frontface, and a thickness between the front face and back face, forming fouredges around the front and back faces, wherein the glass sheet comprisesbetween about 50 mol % to about 90 mol % SiO₂, between about 0 mol % toabout 20 mol % Al₂O₃, 0 mol % to about 20 mol % B₂O₃, and about 0 mol %to about 19 mol % R_(x)O, wherein R is any one or more of Li, Na, K, Rb,Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the glassproduces less than or equal to 2 dB/500 mm absorption. This glassarticle can include R_(x)O—Al₂O₃>0. This glass article can include0<R_(x)O—Al₂O₃<15. This glass article can include x=2 and whereinR₂O—Al₂O₃<15. This glass article can include R₂O Al₂O₃<2. This glassarticle can include x=2 and wherein R₂O—Al₂O₃—MgO>−10. This glassarticle can include 0<(R_(x)O—Al₂O₃)<12, −1<(R₂O—Al₂O₃)<11, and−10<(R₂O—Al₂O₃—MgO)<11. This glass article can include −1<(R₂O—Al₂O₃)<2and −6<(R₂O—Al₂O₃—MgO)<1. This glass article can be a light guide plate.This glass article can include a roughness of at least one face is lessthan 0.6 nm. This glass article can include a thickness of the platebetween about 0.5 mm and about 8 mm. This glass article can include athickness having a variation of less than 5%. This glass article caninclude a light guide plate manufactured from a fusion draw process,slot draw process, or a float process. This glass article can include atleast 10% of the iron is Fe²⁺. This glass article can include a liquidusviscosity greater than 100 kP and a T_(200P) temperature below 1760° C.This glass article can include less than 1 ppm each of Co, Ni, and Cr.This glass article can include a concentration of Fe is <about 50 ppm.This glass article can include a concentration of Fe is <about 20 ppm.This glass article can include a concentration of Fe is <about 10 ppm.This glass article can include Fe+30Cr+35Ni<about 60 ppm. This glassarticle can include Fe+30Cr+35Ni<about 40 ppm. This glass article caninclude Fe+30Cr+35Ni<about 20 ppm. This glass article can includeFe+30Cr+35Ni<about 10 ppm. This glass article can include at least oneedge being a light injection edge that scatters light within an angleless than 12.8 degrees full width half maximum (FWHM) in transmission.This glass article can include a light injection edge that isunpolished. This glass article can include a second edge adjacent to thelight injection edge and a third edge opposite the second edge andadjacent to the light injection edge, wherein the second edge and thethird edge scatter light within an angle of less than 12.8 degrees FWHMin reflection. This glass article can include a second edge and thirdedge having a diffusion angle in reflection that is below 6.4 degrees.This glass article can include a transmittance at 450 nm with at least500 mm in length is greater than or equal to 85%, a transmittance at 550nm with at least 500 mm in length is greater than or equal to 90%, or atransmittance at 630 nm with at least 500 mm in length is greater thanor equal to 85%, and combinations thereof. This glass article caninclude a density is between about 1.95 gm/cc @ 20 C to about 2.7 gm/cc@ 20 C. This glass article can include a Young's modulus between about62 GPa to about 90 GPa. This glass article can include a CTE (0-300° C.)between about 30×10-7/° C. to about 95×10-7/° C. This glass article caninclude a density between about 1.95 gm/cc @ 20 C to about 2.7 gm/cc @20 C, a Young's modulus between about 62 GPa to about 90 GPa, and CTE(0-300° C.) between about 30×10-7/° C. to about 95×10-7/° C. This glassarticle can be chemically strengthened.

Further embodiments include a glass article, comprising a glass sheetwith a front face having a width and a height, a back face opposite thefront face, and a thickness between the front face and back face,forming four edges around the front and back faces, wherein the glasssheet comprises between about 60 mol % to about 80 mol % SiO₂, betweenabout 0.1 mol % to about 15 mol % Al₂O₃, 0 mol % to about 10 mol % B₂O₃,and about 0.1 mol % to about 15 mol % R2O and about 0.1 mol % to about12 mol % RO, wherein R is any one or more of Li, Na, K, Rb, Cs and x is2, or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the glass producesless than or equal to 2 dB/500 mm absorption. This glass article caninclude Fe+30Cr+35Ni<about 60 ppm. This glass article can includeFe+30Cr+35Ni<about 40 ppm. This glass article can includeFe+30Cr+35Ni<about 30 ppm. This glass article can includeFe+30Cr+35Ni<about 20 ppm. This glass article can include0<(R_(x)O—Al₂O₃)<12, −2<(R₂O—Al₂O₃)<11, and −10<(R₂O—Al₂O₃—MgO)<11. Thisglass article can produce less than or equal to 0.5 dB/500 mmabsorption. This glass article can produce less than or equal to 0.25dB/500 mm absorption.

Additional embodiments include a glass article comprising a glass sheethaving between about 50 mol % to about 90 mol % SiO₂, between about 0mol % to about 15 mol % Al₂O₃, between about 0 mol % to about 10 mol %B₂O₃, and about 2 mol % to about 19 mol % R_(x)O, wherein R is any oneor more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and xis 1, and wherein Fe+30Cr+35Ni<about 60 ppm.

Further embodiments include a light guide plate, comprising a glasssheet having between about 0 mol % to about 15 mol % Al₂O₃, and about 0mol % to about 19 mol % R_(x)O, wherein R is any one or more of Li, Na,K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein Feis <about 50 ppm. This light guide plate can include between about 50mol % to about 90 mol % SiO₂ and between about 0 mol % to about 10 mol %B₂O₃. This light guide plate can include less than 1 ppm of each of Co,Ni, and Cr. This light guide plate can produce less than or equal to 2dB/500 mm of light attenuation. This light guide plate can produce lessthan or equal to 1 dB/500 mm absorption. This light guide plate canproduce less than or equal to 0.5 dB/500 mm absorption. This light guideplate can include Fe+30Cr+35Ni<about 60 ppm. This light guide plate caninclude Fe+30Cr+35Ni<about 20 ppm. This light guide plate can includethe mol % of Al₂O₃ is <or substantially equal to the mol % R_(x)O. Thislight guide plate can include R_(x)O—Al₂O₃>0. This light guide plate caninclude 0<R_(x)O—Al₂O₃<15. This light guide plate can include x=2 andwherein R₂O—Al₂O₃<15. This light guide plate can include R₂O—Al₂O₃<2.This light guide plate can include x=2 and wherein R₂O—Al₂O₃—MgO>−10.This light guide plate can include 0<(R_(x)O—Al₂O₃)<12,−1<(R₂O—Al₂O₃)<11, and −10<(R₂O—Al₂O₃—MgO)<11. This light guide platecan include −1<(R₂O—Al₂O₃)<2 and −6<(R₂O—Al₂O₃—MgO)<1. This light guideplate can include a transmittance at 450 nm with at least 500 mm inlength is greater than or equal to 85%, a transmittance at 550 nm withat least 500 mm in length is greater than or equal to 90%, or atransmittance at 630 nm with at least 500 mm in length is greater thanor equal to 85%, and combinations thereof. This light guide plate caninclude a concentration of Fe is <about 20 ppm. This light guide platecan include a concentration of Fe is <about 10 ppm. This light guideplate can be chemically strengthened. In additional embodiments, adisplay device comprising the light guide plate above wherein the lightguide plate further comprises a glass sheet with a front face having awidth and a height, a back face opposite the front face, and a thicknessbetween the front face and back face, forming four edges around thefront and back faces, and wherein one or more edges of the light guideplate are illuminated by a light source. This display device can includea light source selected from the group consisting of an LED, CCFL, OLED,and combinations thereof. This display device can include glasscomprising less than 1 ppm of each of Co, Ni, and Cr. This displaydevice can produce less than or equal to 2 dB/500 mm of lightattenuation. This display device can include Fe+30Cr+35Ni<about 60 ppm.This display device can include the mol % of Al₂O₃ is <or substantiallyequal to the mol % R_(x)O. This display device can include a thicknessof less than 5 mm. This display device can include a transmittance at450 nm with at least 500 mm in length is greater than or equal to 85%, atransmittance at 550 nm with at least 500 mm in length is greater thanor equal to 90%, or a transmittance at 630 nm with at least 500 mm inlength is greater than or equal to 85%, and combinations thereof. Thisdisplay device can include a concentration of Fe is <about 20 ppm.

In some embodiments, a glass article is provided comprising a glasssheet having between about 50 mol % to about 90 mol % SiO₂, betweenabout 0 mol % to about 15 mol % Al₂O₃, between about 0 mol % to about 10mol % B₂O₃, and about 2 mol % to about 19 mol % R_(x)O, wherein R is anyone or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba andx is 1, and wherein the glass produces 2 dB/500 mm or less of lightattenuation in the glass sheet.

In other embodiments, a display device is provided comprising a lightguide plate comprising a glass sheet having a Young's modulus of betweenabout 62 GPa to about 78 GPa, wherein the glass sheet comprises betweenabout 0 mol % to about 15 mol % Al₂O₃ and about 2 mol % to about 19 mol% R_(x)O, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2,or Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the transmittance of theglass sheet at 450 nm with at least 500 mm in length is greater than orequal to 85%, the transmittance of the glass sheet at 550 nm with atleast 500 mm in length is greater than or equal to 90%, or thetransmittance of the glass sheet at 630 nm with at least 500 mm inlength is greater than or equal to 85%. This display device can includea concentration of Fe of the glass sheet is <about 50 ppm. This displaydevice can include a concentration of Fe of the glass sheet is <about 20ppm. This display device can include a concentration of Fe of the glasssheet is <about 10 ppm. This display device can include a thickness lessthan 5 mm.

In some embodiments, a glass article is provided comprising a glasssheet having a Young's modulus of between about 62 GPa to about 78 GPa,wherein the glass sheet comprises between about 0 mol % to about 15 mol% Al₂O₃ and about 2 mol % to about 19 mol % R_(x)O, wherein R is any oneor more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba, and xis 1, and wherein the transmittance of the glass sheet at 450 nm with atleast 500 mm in length is greater than or equal to 85%, thetransmittance of the glass sheet at 550 nm with at least 500 mm inlength is greater than or equal to 90%, or the transmittance of theglass sheet at 630 nm with at least 500 mm in length is greater than orequal to 85%. This glass article can include a concentration of Fe ofthe glass sheet is <about 50 ppm. This glass article can include aconcentration of Fe of the glass sheet is <about 20 ppm. This glassarticle can include a concentration of Fe of the glass sheet is <about10 ppm. This glass article can be a light guide plate. In otherembodiments, a display device comprising the light guide plate describeabove wherein the light guide plate further comprises a glass sheet witha front face having a width and a height, a back face opposite the frontface, and a thickness between the front face and back face, forming fouredges around the front and back faces, and wherein one or more edges ofthe light guide plate are illuminated by a light source.

In further embodiments a glass article is provided comprising a glasssheet having between about 0 mol % to about 15 mol % Al₂O₃, and about 2mol % to about 19 mol % R_(x)O, wherein R is any one or more of Li, Na,K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1, whereinR_(x)O—Al₂O₃ is <15, and wherein the transmittance of the glass sheet at450 nm with at least 500 mm in length is greater than or equal to 85%,the transmittance of the glass sheet at 550 nm with at least 500 mm inlength is greater than or equal to 90%, or the transmittance of theglass sheet at 630 nm with at least 500 mm in length is greater than orequal to 85%. This glass article can include a concentration of Fe ofthe glass sheet is <about 50 ppm. This glass article can include aconcentration of Fe of the glass sheet is <about 20 ppm. This glassarticle can include a concentration of Fe of the glass sheet is <about10 ppm. This glass article can include x=2 and R_(x)O—Al₂O₃<12. Thisglass article can include R_(x)O—Al₂O₃>0. This glass article can includeR₂O—Al₂O₃<2. This glass article can include x=2 and whereinR₂O—Al₂O₃—MgO>−10. This glass article can include 0<(R_(x)O—Al₂O₃)<12,−1<(R₂O—Al₂O₃)<11, and −10<(R₂O—Al₂O₃—MgO)<11. This glass article caninclude −1<(R₂O—Al₂O₃)<2 and −6<(R₂O—Al₂O₃—MgO)<1.

In additional embodiments, a glass article is provided comprising aglass sheet having between about 50 mol % to about 90 mol % SiO₂,between about 0 mol % to about 15 mol % Al₂O₃, between about 0 mol % toabout 10 mol % B₂O₃, and about 0 mol % to about 19 mol % R_(x)O, whereinR is any one or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sror Ba and x is 1, wherein the glass produces 2 dB/500 mm or less oflight attenuation in the glass sheet, and wherein 0<(R_(x)O—Al₂O₃)<12,−2<(R₂O—Al₂O₃)<11, and −10<(R₂O—Al₂O₃—MgO)<11. This glass article caninclude a concentration of Fe of the glass sheet is <about 50 ppm. Thisglass article can include Fe+30Cr+35Ni<about 60 ppm. This glass articlecan include a T_(200P) temperature below 1760° C. This glass article caninclude a T_(200P) temperature below 1730° C. This glass article caninclude a T_(200P) temperature below 1700° C. This glass article caninclude a liquidus viscosity greater than 100kP. This glass article caninclude a liquidus viscosity greater than 500kP.

It will be appreciated that the various disclosed embodiments mayinvolve particular features, elements or steps that are described inconnection with that particular embodiment. It will also be appreciatedthat a particular feature, element or step, although described inrelation to one particular embodiment, may be interchanged or combinedwith alternate embodiments in various non-illustrated combinations orpermutations.

It is also to be understood that, as used herein the terms “the,” “a,”or “an,” mean “at least one,” and should not be limited to “only one”unless explicitly indicated to the contrary. Thus, for example,reference to “a ring” includes examples having two or more such ringsunless the context clearly indicates otherwise. Likewise, a “plurality”or an “array” is intended to denote “more than one.” As such, a“plurality of droplets” includes two or more such droplets, such asthree or more such droplets, etc., and an “array of rings” comprises twoor more such droplets, such as three or more such rings, etc.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, examples include from the one particular value and/or to theother particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another aspect. It will be furtherunderstood that the endpoints of each of the ranges are significant bothin relation to the other endpoint, and independently of the otherendpoint.

The terms “substantial,” “substantially,” and variations thereof as usedherein are intended to note that a described feature is equal orapproximately equal to a value or description. For example, a“substantially planar” surface is intended to denote a surface that isplanar or approximately planar. Moreover, as defined above,“substantially similar” is intended to denote that two values are equalor approximately equal. In some embodiments, “substantially similar” maydenote values within about 10% of each other, such as within about 5% ofeach other, or within about 2% of each other.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatany particular order be inferred.

While various features, elements or steps of particular embodiments maybe disclosed using the transitional phrase “comprising,” it is to beunderstood that alternative embodiments, including those that may bedescribed using the transitional phrases “consisting” or “consistingessentially of,” are implied. Thus, for example, implied alternativeembodiments to a device that comprises A+B+C include embodiments where adevice consists of A+B+C and embodiments where a device consistsessentially of A+B+C.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present disclosurewithout departing from the spirit and scope of the disclosure. Sincemodifications combinations, sub-combinations and variations of thedisclosed embodiments incorporating the spirit and substance of thedisclosure may occur to persons skilled in the art, the disclosureshould be construed to include everything within the scope of theappended claims and their equivalents.

Examples

The following examples are set forth below to illustrate the methods andresults according to the disclosed subject matter. These examples arenot intended to be inclusive of all embodiments of the subject matterdisclosed herein, but rather to illustrate representative methods andresults. These examples are not intended to exclude equivalents andvariations of the present disclosure which are apparent to one skilledin the art.

Efforts have been made to ensure accuracy with respect to numbers (e.g.,amounts, temperature, etc.) but some errors and deviations should beaccounted for. Unless indicated otherwise, temperature is in ° C. or isat ambient temperature, and pressure is at or near atmospheric. Thecompositions themselves are given in mole percent on an oxide basis andhave been normalized to 100%. There are numerous variations andcombinations of reaction conditions, e.g., component concentrations,temperatures, pressures and other reaction ranges and conditions thatcan be used to optimize the product purity and yield obtained from thedescribed process. Only reasonable and routine experimentation will berequired to optimize such process conditions.

The glass properties set forth in Table 1 were determined in accordancewith techniques conventional in the glass art. Thus, the linearcoefficient of thermal expansion (CTE) over the temperature range25-300° C. is expressed in terms of ×10-7/° C. and the annealing pointis expressed in terms of ° C. These were determined from fiberelongation techniques (ASTM references E228-85 and C336, respectively).The density in terms of grams/cm3 was measured via the Archimedes method(ASTM C693). The melting temperature in terms of ° C. (defined as thetemperature at which the glass melt demonstrates a viscosity of 200poises) was calculated employing a Fulcher equation fit to hightemperature viscosity data measured via rotating cylinders viscometry(ASTM C965-81).

The liquidus temperature of the glass in terms of ° C. was measuredusing the standard gradient boat liquidus method of ASTM C829-81. Thisinvolves placing crushed glass particles in a platinum boat, placing theboat in a furnace having a region of gradient temperatures, heating theboat in an appropriate temperature region for 24 hours, and determiningby means of microscopic examination the highest temperature at whichcrystals appear in the interior of the glass. More particularly, theglass sample is removed from the Pt boat in one piece, and examinedusing polarized light microscopy to identify the location and nature ofcrystals which have formed against the Pt and air interfaces, and in theinterior of the sample. Because the gradient of the furnace is very wellknown, temperature vs. location can be well estimated, within 5-10° C.The temperature at which crystals are observed in the internal portionof the sample is taken to represent the liquidus of the glass (for thecorresponding test period). Testing is sometimes carried out at longertimes (e.g. 72 hours), to observe slower growing phases. The liquidusviscosity in poises was determined from the liquidus temperature and thecoefficients of the Fulcher equation. If included, Young's modulusvalues in terms of GPa were determined using a resonant ultrasonicspectroscopy technique of the general type set forth in ASTM E1875-00e1.

The exemplary glasses of Table 1 were prepared using a commercial sandas a silica source, milled such that 90% by weight passed through astandard U.S. 100 mesh sieve. Alumina was the alumina source, periclasewas the source for MgO, limestone the source for CaO, strontiumcarbonate, strontium nitrate or a mix thereof was the source for SrO,barium carbonate was the source for BaO, and tin (IV) oxide was thesource for SnO2. The raw materials were thoroughly mixed, loaded into aplatinum vessel suspended in a furnace heated by silicon carbideglowbars, melted and stirred for several hours at temperatures between1600 and 1650° C. to ensure homogeneity, and delivered through anorifice at the base of the platinum vessel. The resulting patties ofglass were annealed at or near the annealing point; and then subjectedto various experimental methods to determine physical, viscous andliquidus attributes.

These methods are not unique, and the glasses of Table 1 can be preparedusing standard methods well-known to those skilled in the art. Suchmethods include a continuous melting process; such as would be performedin a continuous melting process, wherein the melter used in thecontinuous melting process is heated by gas, by electric power, orcombinations thereof.

Raw materials appropriate for producing exemplary glasses includecommercially available sands as sources for SiO2; alumina, aluminumhydroxide, hydrated forms of alumina, and various aluminosilicates,nitrates and halides as sources for Al2O3; boric acid, anhydrous boricacid and boric oxide as sources for B2O3; periclase, dolomite (also asource of CaO), magnesia, magnesium carbonate, magnesium hydroxide, andvarious forms of magnesium silicates, aluminosilicates, nitrates andhalides as sources for MgO; limestone, aragonite, dolomite (also asource of MgO), wolastonite, and various forms of calcium silicates,aluminosilicates, nitrates and halides as sources for CaO; and oxides,carbonates, nitrates and halides of strontium and barium. If a chemicalfining agent is desired, tin can be added as SnO2, as a mixed oxide withanother major glass component (e.g., CaSnO3), or in oxidizing conditionsas SnO, tin oxalate, tin halide, or other compounds of tin known tothose skilled in the art.

The glasses in Table 1 contain SnO2 as a fining agent, but otherchemical fining agents could also be employed to obtain glass ofsufficient quality for TFT substrate applications. For example,exemplary glasses could employ any one or combinations of As2O3, Sb2O3,CeO2, Fe2O3, and halides as deliberate additions to facilitate fining,and any of these could be used in conjunction with the SnO2 chemicalfining agent shown in the examples. Of these, As2O3 and Sb2O3 aregenerally recognized as hazardous materials, subject to control in wastestreams such as might be generated in the course of glass manufacture orin the processing of TFT panels. It is therefore desirable to limit theconcentration of As2O3 and Sb2O3 individually or in combination to nomore than 0.005 mol %.

In addition to the elements deliberately incorporated into exemplaryglasses, nearly all stable elements in the periodic table are present inglasses at some level, either through low levels of contamination in theraw materials, through high-temperature erosion of refractories andprecious metals in the manufacturing process, or through deliberateintroduction at low levels to fine tune the attributes of the finalglass. For example, zirconium may be introduced as a contaminant viainteraction with zirconium-rich refractories. As a further example,platinum and rhodium may be introduced via interactions with preciousmetals. As a further example, iron may be introduced as a tramp in rawmaterials, or deliberately added to enhance control of gaseousinclusions. As a further example, manganese may be introduced to controlcolor or to enhance control of gaseous inclusions. As a further example,alkalis may be present as a tramp component at levels up to about 0.1mol % for the combined concentration of Li2O, Na2O and K2O.

Hydrogen is inevitably present in the form of the hydroxyl anion, OH—,and its presence can be ascertained via standard infrared spectroscopytechniques. Dissolved hydroxyl ions significantly and nonlinearly impactthe annealing point of exemplary glasses, and thus to obtain the desiredannealing point it may be necessary to adjust the concentrations ofmajor oxide components so as to compensate. Hydroxyl ion concentrationcan be controlled to some extent through choice of raw materials orchoice of melting system. For example, boric acid is a major source ofhydroxyls, and replacing boric acid with boric oxide can be a usefulmeans to control hydroxyl concentration in the final glass. The samereasoning applies to other potential raw materials comprising hydroxylions, hydrates, or compounds comprising physisorbed or chemisorbed watermolecules. If burners are used in the melting process, then hydroxylions can also be introduced through the combustion products fromcombustion of natural gas and related hydrocarbons, and thus it may bedesirable to shift the energy used in melting from burners to electrodesto compensate. Alternatively, one might instead employ an iterativeprocess of adjusting major oxide components so as to compensate for thedeleterious impact of dissolved hydroxyl ions.

Sulfur is often present in natural gas, and likewise is a trampcomponent in many carbonate, nitrate, halide, and oxide raw materials.In the form of SO2, sulfur can be a troublesome source of gaseousinclusions. The tendency to form SO2-rich defects can be managed to asignificant degree by controlling sulfur levels in the raw materials,and by incorporating low levels of comparatively reduced multivalentcations into the glass matrix. While not wishing to be bound by theory,it appears that SO2-rich gaseous inclusions arise primarily throughreduction of sulfate (SO4=) dissolved in the glass. The elevated bariumconcentrations of exemplary glasses appear to increase sulfur retentionin the glass in early stages of melting, but as noted above, barium isrequired to obtain low liquidus temperature, and hence high T35k-Tliqand high liquidus viscosity. Deliberately controlling sulfur levels inraw materials to a low level is a useful means of reducing dissolvedsulfur (presumably as sulfate) in the glass. In particular, sulfur ispreferably less than 200 ppm by weight in the batch materials, and morepreferably less than 100 ppm by weight in the batch materials.

Reduced multivalents can also be used to control the tendency ofexemplary glasses to form SO2 blisters. While not wishing to be bound totheory, these elements behave as potential electron donors that suppressthe electromotive force for sulfate reduction. Sulfate reduction can bewritten in terms of a half reaction such as

SO4=→SO2+02+2e−

where e− denotes an electron. The “equilibrium constant” for the halfreaction is

Keq=[SO2][O2][e−]2/[SO4=]

where the brackets denote chemical activities. Ideally one would like toforce the reaction so as to create sulfate from SO2, O2 and 2e−. Addingnitrates, peroxides, or other oxygen-rich raw materials may help, butalso may work against sulfate reduction in the early stages of melting,which may counteract the benefits of adding them in the first place. SO2has very low solubility in most glasses, and so is impractical to add tothe glass melting process. Electrons may be “added” through reducedmultivalents. For example, an appropriate electron-donating halfreaction for ferrous iron (Fe2+) is expressed as

2Fe2+→2Fe3++2e−

This “activity” of electrons can force the sulfate reduction reaction tothe left, stabilizing SO4=in the glass. Suitable reduced multivalentsinclude, but are not limited to, Fe2+, Mn2+, Sn2+, Sb3+, As3+, V3+,Ti3+, and others familiar to those skilled in the art. In each case, itmay be important to minimize the concentrations of such components so asto avoid deleterious impact on color of the glass, or in the case of Asand Sb, to avoid adding such components at a high enough level so as tocomplication of waste management in an end-user's process.

In addition to the major oxides components of exemplary glasses, and theminor or tramp constituents noted above, halides may be present atvarious levels, either as contaminants introduced through the choice ofraw materials, or as deliberate components used to eliminate gaseousinclusions in the glass. As a fining agent, halides may be incorporatedat a level of about 0.4 mol % or less, though it is generally desirableto use lower amounts if possible to avoid corrosion of off-gas handlingequipment. In some embodiments, the concentrations of individual halideelements are below about 200 ppm by weight for each individual halide,or below about 800 ppm by weight for the sum of all halide elements.

In addition to these major oxide components, minor and tramp components,multivalents and halide fining agents, it may be useful to incorporatelow concentrations of other colorless oxide components to achievedesired physical, optical or viscoelastic properties. Such oxidesinclude, but are not limited to, TiO2, ZrO2, HfO2, Nb2O5, Ta2O5, MoO3,WO3, ZnO, In2O3, Ga2O3, Bi2O3, GeO2, PbO, SeO3, TeO2, Y₂O₃, La2O3,Gd2O3, and others known to those skilled in the art. Through aniterative process of adjusting the relative proportions of the majoroxide components of exemplary glasses, such colorless oxides can beadded to a level of up to about 2 mol % without unacceptable impact toannealing point, T35k-Tliq or liquidus viscosity.

Table 6 shows examples of glasses (samples 1-69) with hightransmissibility as described herein.

TABLE 6 1 2 3 4 5 6 7 SiO2 74.79 66.86 66.47 69.7 70.92 68.92 70.23Al2O3 7.7 11.97 11.16 8.97 8 11.68 9.95 B2O3 0.93 7.16 9.28 10.21 10.984.69 8.36 Li2O 0 0 0 0 0 0 0 Na2O 12.16 11.32 10.3 8.4 7.41 12.03 9.08K2O 0.01 0.01 0.67 0.01 0.01 0.01 2.26 MgO 4.16 2.5 1.03 2.53 2.51 2.490.03 CaO 0 0.04 0.92 0.04 0.04 0.04 0.03 SrO 0 0 0 0 0 0 0 BaO 0 0 0 0 00 0 SnO2 0.19 0.1 0.1 0.1 0.09 0.1 0.02 Fe2O3 0.05 0.05 0.05 0.05 0.050.05 0.02 ZrO2 0.00 0.00 0.02 0.00 0.00 0 0.02 RxO—Al2O3 8.6 1.9 1.8 2.02.0 2.89 1.5 R2O—Al2O3 4.5 −0.6 −0.2 −0.6 −0.6 0.36 1.4 R2O—( Al2O3 +MgO) 0 −3 −1 −3 −3 −2.13 1 strain 553.2 523.8 529.5 523.9 567.8 anneal607.4 575.2 582.9 577.3 621.6 soft 885.5 848.2 872.3 868 913.3 822.8 CTE65.2 66.3 54.7 51 68.6 70 density 2.366 2.357 2.312 2.295 2.382 2.34 A−3.3E+00 −2.6E+00 −2.7E+00 −2.7E+00 −3.038 −3.5E+00 B  9.1E+03  8.0E+03 8.5E+03  8.6E+03  8948.7  1.1E+04 To 50 67.4414 47.4 36.6 66.9 −246.1T(200P) 1689 1690 1732 1748 1743 1747 72 hr gradient boat int 1050 intliq visc 8 9 10 11 12 13 14 SiO2 68.64 68.6 72.29 65.79 77.7 70.26 70.93Al2O3 9.1 9.15 9.33 11.1 6 8.66 8.63 B2O3 11.16 11.13 1.84 7.11 0 7.597.58 Li2O 0 0 0 0 0 0 0 Na2O 8.69 8.67 12.62 10.17 16.1 7.79 8.08 K2O0.56 0.56 0.01 0.67 0.01 1.16 0.76 MgO 0.89 0.88 3.69 2.53 0.01 2.262.28 CaO 0.79 0.03 0 0.04 0.02 0.04 0.04 SrO 0 0.8 0 2.43 0 2.09 1.56BaO 0 0 0 0 0 0 0 SnO2 0.1 0.1 0.18 0.09 0.1 0.07 0.07 Fe2O3 0.05 0.050.05 0.05 0.05 0.05 0.05 ZrO2 0.02 0.02 0.00 0.02 0.00 0.02 0.02RxO—Al2O3 1.8 1.8 7.0 4.7 10.1 4.7 4.1 R2O—Al2O3 0.2 0.1 3.3 −0.3 10.10.3 0.2 R2O—( Al2O3 + MgO) −1 −1 0 −3 10 −2 −2 strain 508.3 510.1 538.1482.1 536.5 537.8 anneal 557.7 560.6 584.7 527.2 585 587.6 soft 824.4831.2 828.6 747.6 832.3 852.7 CTE 60.4 60.5 68 81 61.3 59.2 density2.324 2.336 2.439 2.398 2.402 2.382 A −2.3E+00 −2.3E+00 −2.3E+00−1.3E+00 −1.9E+00 −2.2E+00 B  7.7E+03  7.6E+03  6.9E+03  5.1E+03 6.5E+03  7.2E+03 To 57.5 65.4 138.2 1.7E+02 152.4 115.6 T(200P) 17301722 1632 1613 1701 1732 72 hr gradient boat int 810 750 1000 925 960int liq visc 83904910 683403477 3295637 2421850 15 16 17 18 19 20 21SiO2 68.54 65.83 68.72 68.69 71.02 76.17 68.62 Al2O3 10.32 12.93 9.1310.07 6.42 6.91 10.28 B2O3 7.24 6.19 7.21 9.12 7.42 5.89 7.17 Li2O 0 0 00 0 0 0 Na2O 9.87 12.32 10.17 9.44 5.68 10.85 9.85 K2O 0.26 0.01 0.630.56 2.28 0.01 0.26 MgO 2.99 2.54 3.04 1.02 2 0 0.72 CaO 0.62 0.04 0.920.93 0.03 0.02 2.95 SrO 0 0 0 0 4.17 0 0 BaO 0 0 0 0 0 0 0 SnO2 0.09 0.10.09 0.1 0.91 0.1 0.08 Fe2O3 0.05 0.05 0.05 0.05 0.05 0.05 0.05 ZrO20.02 0.00 0.02 0.02 0.02 0.00 0.02 RxO—Al2O3 3.4 2.0 5.6 1.9 7.7 4.0 3.5R2O—Al2O3 −0.2 −0.6 1.7 −0.1 1.5 4.0 −0.2 R2O—( Al2O3 + MgO) −3 −3 −1 −10 4 −1 strain 547.5 562.3 531.6 52.4 541.6 539.1 544.2 anneal 598.2614.8 578.1 576.2 587.2 584.8 592.4 soft 872.6 896.7 823 859 798.7 804.3838.4 CTE 62.9 69.6 66.6 62.5 60.1 62.1 63.4 density 2.364 2.383 2.3822.343 2.458 2.374 2.385 A −2.8E+00 −3.3E+00 −1.9E+00 −2.7E+00 −1.4E+00−6.7E−01 −2.0E+00 B  8.4E+03  9.1E+03  6.4E+03  8.5E+03  5.2E+03 4.4E+03  6.7E+03 To 67.1 58.8 152.3 36.4 233.6 275.0909 153.8 T(200P)1721 1680 1671 1731 1646 1744 1702 72 hr gradient boat int 1070 965 810960 int liq visc 407671 1810825 22 23 24 25 26 27 28 SiO2 68.75 70.3170.93 77.13 74.28 72.22 65.33 Al2O3 10.1 8.68 8.67 6.01 5.06 7.62 13.65B2O3 7.36 9.51 7.52 0 3.71 7.58 5 Li2O 0 0 0 0 0 0 0 Na2O 9.41 7.81 8.7911.76 4.17 8.08 13.34 K2O 0.56 1.16 0.01 0.01 0.99 0.01 0 MgO 1.01 1.242.32 4.84 6.05 2.22 2.5 CaO 0.64 0.03 0.04 0 0.06 0.03 0.03 SrO 2.011.11 1.57 0 5.52 2.09 0 BaO 0 0 0 0 0 0 0 SnO2 0.09 0.08 0.08 0.2 0.090.08 0.07 Fe2O3 0.05 0.05 0.05 0.05 0.05 0.05 0.05 ZrO2 0.02 0.02 0.020.00 0.02 0.02 0.02 RxO—Al2O3 3.5 2.7 4.1 10.6 11.7 4.8 2.2 R2O—Al2O3−0.1 0.3 0.1 5.8 0.1 0.5 −0.3 R2O—( Al2O3 + MgO) −1 −1 −2 1 −6 −2 −3strain 539.5 519.4 542.5 582.4 540.8 569.3 anneal 588 568.4 591.4 631.6589.1 624.2 soft 64.4 828.4 859.5 873 836.2 904.1 CTE 834.7 59.7 58.252.1 55.7 72.8 density 2.415 2.353 2.382 2.491 2.389 2.397 A −2.0E+00−1.9E+00 −2.1E+00 −2.1E+00 −1.6E+00 −3.4E+00 B  6.6E+03  6.8E+03 7.0E+03  6.4E+03  6.2E+03  9.2E+03 To 150.8 111.1 133.5 212.7 174.567.9 T(200P) 1701 1741 1731 1676 1738 1676 72 hr gradient boat int 1010830 980 1075 915 1020 int liq visc 41951074 1518435 4822146 29 30 31 3233 34 35 SiO2 68.94 70.14 68.99 64.59 64.53 64.45 71.47 Al2O3 9.06 119.01 13.97 13.14 13.14 6.24 B2O3 7.21 2.8 7.18 5.18 7.29 7.33 7.32 Li2O0 0 0 0 0 0 0 Na2O 10.02 12.88 9.05 13.57 11.19 11.16 4.69 K2O 0.6 0.010.59 0.01 1.5 1.5 1.57 MgO 1.99 3.01 3.05 2.53 1.16 1.17 4.19 CaO 0.04 00.04 0 1.06 1.07 0.05 SrO 1.99 0 1.92 0 0 0 4.31 BaO 0 0 0 0 0 0 0 SnO20.1 0.12 0.09 0.1 0.1 0.1 0.09 Fe2O3 0.05 0.05 0.05 0.05 0.01 0.05 0.05ZrO2 0.02 0.00 0.02 0.00 0.02 0.02 0.02 RxO—Al2O3 5.6 4.9 5.6 2.14 1.81.8 8.6 R2O—Al2O3 1.6 1.9 0.6 −0.39 −0.5 −0.5 0.0 R2O—( Al2O3 + MgO) 0−1 −2 −2.92 −2 −2 −4 strain 532.2 538.5 541.2 538.5 555.6 anneal 578585.7 592.6 591.1 602.9 soft 806 828.8 863.8 869.3 832.5 CTE 66.5 63.373.9 74.2 54.9 density 2.425 2.414 2.4 2.386 2.388 2.453 A −1.6E+00−1.9E+00 −3.1E+00 −3.2E+00 −1.8E+00 B  5.8E+03  6.4E+03  8.6E+03 8.8E+03  6.0E+03 To 188 162.6 57.48595 48.69154 202.4 T(200P) 1662 16691672 1661 1656 72 hr gradient boat int 935 975 1000 int liq visc 36 3738 39 40 41 42 SiO2 72.76 68.29 70.67 72.35 69.58 69.09 72.45 Al2O3 5.0110.78 8.25 7.63 9.72 8.95 7.6 B2O3 8.32 7.35 8.43 8.03 7.48 8.84 7.44Li2O 0 0 0 0 0 0 0 Na2O 4.14 10.17 7.12 7.47 9.2 8.94 8.04 K2O 0.97 0.261.04 0.01 0.42 0.01 0 MgO 4.31 2.44 2.22 2.23 2.37 2.97 0 CaO 0.05 0.040.04 0.03 0.03 0.04 0.02 SrO 4.27 0.53 2.08 2.09 1.06 1.01 0 BaO 0 0 0 00 0 4.3 SnO2 0.09 0.08 0.07 0.07 0.07 0.08 0.08 Fe2O3 0.05 0.05 0.050.05 0.05 0.05 0.05 ZrO2 0.02 0.02 0.02 0.02 0.02 0.02 0.02 RxO—Al2O38.7 2.7 4.3 4.2 3.4 4.0 4.8 R2O—Al2O3 0.1 −0.4 −0.1 −0.2 −0.1 0.0 0.4R2O—( Al2O3 + MgO) −4 −3 −2 −2 −2 −3 0.4 strain 556.7 547.1 535.2 541.6542 535.3 552.1 anneal 605.8 599.8 583.8 590.2 593.2 583.8 597 soft831.7 881.1 834.9 854.2 872.5 845.3 801.3 CTE 49.6 63.5 57.7 53 60.957.9 58.8 density 2.433 2.369 2.387 2.378 2.375 2.367 2.53 A −1.7E+00−3.0E+00 −1.9E+00 −2.1E+00 −2.4E+00 −2.4E+00 −9.6E−01 B  5.9E+03 8.8E+03  6.6E+03  7.0E+03  7.7E+03  7.5E+03  4.6E+03 To 212.6 55.9142.2 127.6 97.6 101.1 281.5 T(200P) 1679 1711 1728 1738 1727 1696 167772 hr gradient boat int 1000 1020 935 970 1010 1050 875 int liq visc1230646 3059865 1956914 1029006 307651 5133820 43 44 45 46 47 48 49 SiO272.33 65.25 68.19 77.36 72.16 72.4 72.25 Al2O3 7.7 13.64 10.84 6.34 7.687.52 7.64 B2O3 7.6 5.12 7.37 1.99 7.63 7.51 7.59 Li2O 0 0 0 0 0 0 0 Na2O8.12 13.32 10.47 14.13 6.98 8.07 8.14 K2O 0 0 0.01 0.01 1.04 0.01 0 MgO1.41 2.49 2.42 0 2.25 3.21 4.21 CaO 1.21 0.03 0.04 0.03 0.04 0.04 0.02SrO 1.47 0 0.53 0 2.09 1.1 0 BaO 0 0 0 0 0 0 0 SnO2 0.08 0.07 0.07 0.090.07 0.08 0.08 Fe2O3 0.05 0.05 0.05 0.05 0.05 0.05 0.05 ZrO2 0.02 0.020.02 0.00 0.02 0.02 0.02 RxO—Al2O3 4.5 2.2 2.6 7.8 4.7 4.9 4.7 R2O—Al2O30.4 −0.3 −0.4 7.8 0.3 0.6 0.5 R2O—(Al2O3 + MgO) −1 −3 −3 8 −2 −3 −4strain 548.3 574.1 547.8 507 539.6 540.9 557.8 anneal 595.9 628.6 600.2551.4 588.1 589.5 610.1 soft 834.4 910.1 881.8 764.7 840.8 855.4 880.6CTE 55.7 73.5 63.2 74 56.8 54.5 54.5 density 2.382 2.397 2.369 2.4062.388 2.364 2.332 A −1.7E+00 −3.3E+00 −2.8E+00 0.0E+00 −1.9E+00 −2.0E+00−2.3E+00 B  6.2E+03  8.9E+03  8.4E+03  0.0E+00  6.6E+03  7.0E+03 7.4E+03 To 178.2 87.5 75.5 0.0E+00 149.6 125.5 134.4 T(200P) 1745 16871708 0 1719 1745 1756 72 hr gradient boat int 930 1020 1000 930 10501140 int liq visc 4203276 1747638 3548343 364209 124087 50 51 52 53 5455 56 SiO2 69.86 69.17 67.89 64.62 67.94 72.43 69.67 Al2O3 8.56 8.978.56 13.85 10.68 7.63 9.7 B2O3 10.12 7.25 10.16 5.22 7.19 7.47 7.44 Li2O0 0 0 0 0 0 0 Na2O 8.54 10.45 8.48 13.6 10.88 8.04 9.54 K2O 0.01 0.010.01 0.01 0.01 0 0.05 MgO 1.38 2.95 2.37 2.52 2.32 0.04 2.36 CaO 0.030.04 0.04 0.04 0.04 4.24 0.04 SrO 1.36 1.01 2.35 0 0.81 0 1.06 BaO 0 0 00 0 0 0 SnO2 0.07 0.08 0.07 0.08 0.07 0.08 0.07 Fe2O3 0.05 0.05 0.050.05 0.05 0.05 0.05 ZrO2 0.02 0.02 0.02 0.02 0.02 0.02 0.02 RxO—Al2O32.8 5.5 4.7 2.3 3.4 4.7 3.4 R2O—Al2O3 0.0 1.5 −0.1 −0.2 0.2 0.4 −0.1R2O—( Al2O3 + MgO) −1 −1 −2 −3 −2 0 −2 strain 520.8 535.1 528.8 570.4542 559.6 543.8 anneal 569.8 581.6 575.9 623.9 591.2 507.4 594.7 soft823.5 825 803.8 899.6 856.8 834.5 878.8 CTE 56.4 63.9 57.9 73.8 65.256.5 60.4 density 2.354 2.396 2.398 2.4 2.386 2.372 2.376 A −2.1E+00−1.8E+00 −1.9E+00 −3.4E+00 −2.6E+00 −1.3E+00 −2.4E+00 B  7.1E+03 6.2E+03  6.2E+03  9.0E+03  7.9E+03  5.2E+03  7.7E+03 To 103.1 168.2165.5 79.1 89.5 253.5 100.1 T(200P) 1718 1680 1635 1668 1692 1704 172772 hr gradient boat int 890 940 925 1015 975 980 1010 int liq visc1655694 1878562 759047 1089696 57 58 59 60 61 62 63 SiO2 72.24 72.172.27 70.16 70.17 69.3 76.83 Al2O3 7.42 7.42 7.66 8.97 8.95 9.77 6.64B2O3 7.49 7.39 7.61 7.22 7.17 7.07 3.81 Li2O 0 0 0 0 0 0 0 Na2O 8.579.01 7.95 10.47 8.94 10.9 12.54 K2O 0 0 0 0.01 0.01 0 0.01 MgO 2.1 2 01.99 3.57 1.92 0 CaO 0.02 0.02 0.02 0.03 0.04 0.91 0.02 SrO 2.02 1.914.35 1.01 1.01 0 0 BaO 0 0 0 0 0 0 0 SnO2 0.08 0.08 0.07 0.08 0.08 0.080.1 Fe2O3 0.05 0.05 0.05 0.05 0.05 0.05 0.05 ZrO2 0.02 0.02 0.02 0.020.02 0.02 0.00 RxO—Al2O3 5.3 5.5 4.7 4.5 4.6 4.0 5.9 R2O—Al2O3 1.2 1.60.3 1.5 0.0 1.1 5.9 R2O—(Al2O3 + MgO) −1 0 0 0 −4 −1 6 strain 551 533.9547.3 530.4 anneal 596.6 580.6 596.5 574.9 soft 823 816.4 814.2 822.3860.6 844.3 782.6 CTE 58.4 57.1 57.1 63.6 58.5 65.3 68.4 density 2.3932.397 2.454 2.389 2.376 2.371 2.403 A −1.1E+00 −1.7E+00 −2.4E+00−7.6E−01 B  4.9E+03  6.2E+03  7.5E+03  4.3E+03 To 259.3 165.5 111.6 2.7E+02 T(200P) 1701 1695 1707 1682 72 hr gradient boat int 920 9301110 int liq visc 2065037 2181126 132055 64 65 66 67 68 69 SiO2 68.6668.52 67.75 67.91 68.93 72.4 Al2O3 10.09 11.14 12.68 10.97 9.99 7.03B2O3 7.25 7.25 3.7 8.07 9.06 7.54 Li2O 0 0 0 0 0 0 Na2O 10.24 10.33 13.310.34 9.36 8.57 K2O 0.65 0.67 0.01 0.01 0.01 0 MgO 2.02 1.01 2.43 2.52.48 2.21 CaO 0.92 0.92 0 0.04 0.04 0.02 SrO 0 0 0 0 0 2.09 BaO 0 0 0 00 0 SnO2 0.1 0.09 0.09 0.1 0.09 0.08 Fe2O3 0.05 0.05 0.05 0.05 0.05 0.05ZrO2 0.02 0.02 0.00 0.00 0.00 0.02 RxO—Al2O3 3.7 1.8 3.060 1.9 1.9 5.9R2O—Al2O3 0.8 −0.1 0.6 −0.6 −0.6 1.5 R2O—(Al2O3 + MgO) −1 −1 −1.8 −3 −3−1 strain 536.1 540.3 576.5 547.2 537.1 anneal 585.1 592.5 630.8 601.3589.6 soft 842.9 874.7 883.9 874.6 814.5 CTE 66.4 66.1 62.1 58.3 57.3density 2.373 2.364 2.403 2.351 2.333 2.397 A −2.2E+00 −2.9E+00 −3.2−3.0E+00 −3.1E+00 B  7.1E+03  8.7E+03 9081.6  8.8E+03  9.2E+03 To 120.645.4 75.4 58.3 20.4 T(200P) 1701 1724 1726 1706 1727 72 hr gradient boatint 920 940 int liq visc 7235117

What is claimed is:
 1. A glass article, comprising: a glass sheet with afront face having a width and a height, a back face opposite the frontface, and a thickness between the front face and back face, wherein theglass sheet comprises from about 50 mol % to about 90 mol % SiO₂, fromabout 0 mol % to about 20 mol % Al₂O₃, from about 5 mol % to about 20mol % B₂O₃, and from about 0 mol % to about 25 mol % R_(x)O, wherein Ris any one or more of Li, Na, K, Rb, Cs and x is 2, or R is any one ormore of Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the glass producesless than or equal to 2 dB/500 mm absorption.
 2. The glass article ofclaim 1, wherein R_(x)O—Al₂O₃>0.
 3. The glass article of claim 1,wherein 0<R_(x)O—Al₂O₃<15.
 4. The glass article of claim 1, wherein x=2and wherein R₂O—Al₂O₃<15.
 5. The glass article of claim 4, whereinR₂O—Al₂O₃<2.
 6. The glass article of claim 1, wherein x=2 and whereinR₂O—Al₂O₃—MgO>−15.
 7. The glass article of claim 1, wherein0<(R_(x)O—Al₂O₃)<25, −11<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃—MgO)<11. 8.The glass article of claim 1, wherein −1<(R₂O—Al₂O₃)<2 and−6<(R₂O—Al₂O₃—MgO)<1.
 9. The glass article of claim 1, wherein the glasscomprises less than 1 ppm each of Co, Ni, and Cr.
 10. The glass articleof claim 1, wherein a concentration of Fe is <about 50 ppm.
 11. Theglass article of claim 1, wherein a concentration of Fe is <about 20ppm.
 12. The glass article of claim 1, wherein a concentration of Fe is<about 10 ppm.
 13. The glass article of claim 10, wherein at least 10%of the Fe is Fe²⁺.
 14. The glass article of claim 1, whereinFe+30Cr+35Ni<about 60 ppm.
 15. The glass article of claim 1, whereinFe+30Cr+35Ni<about 40 ppm.
 16. The glass article of claim 1, whereinFe+30Cr+35Ni<about 20 ppm.
 17. The glass article of claim 1, whereinFe+30Cr+35Ni<about 10 ppm.
 18. The glass article of claim 1, comprisinga transmittance at 450 nm with at least 500 mm in length greater than orequal to 85%, a transmittance at 550 nm with at least 500 mm in lengthgreater than or equal to 90%, or a transmittance at 630 nm with at least500 mm in length greater than or equal to 85%, and combinations thereof.19. The glass article of claim 1, comprising a density ranging fromabout 1.95 gm/cc to about 2.7 gm/cc at 20° C.
 20. The glass article ofclaim 1, comprising a Young's modulus ranging from about 62 GPa to about90 GPa.
 21. The glass article of claim 1, comprising a CTE (0-300° C.)ranging from about 30×10⁻⁷/° C. to about 95×10⁻⁷ I° C.
 22. The glassarticle of claim 1, comprising a density ranging from about 1.95 gm/ccto about 2.7 gm/cc at 20° C., a Young's modulus ranging from about 62GPa to about 90 GPa, and a CTE (0-300° C.) ranging from about 30×10⁻⁷/°C. to about 95×10⁻⁷/° C.
 23. The glass article of claim 1, wherein theglass sheet is chemically strengthened.
 24. The glass article of claim1, comprising a T_(200P) temperature below 1760° C.
 25. The glassarticle of claim 1, comprising a liquidus viscosity greater than 100kP.26. The glass article of claim 1, comprising a liquidus viscositygreater than 500kP.
 27. The glass article of claim 1, wherein the glassarticle is a light guide plate.
 28. The glass article of claim 27,wherein a roughness of at least one face is less than 0.6 nm.
 29. Theglass article of claim 27, wherein a thickness of the light guide plateranges from about 0.5 mm to about 8 mm.
 30. The glass article of claim27, comprising at least one light injection edge that scatters lightwithin an angle less than 12.8 degrees full width half maximum (FWHM) intransmission.
 31. The glass article of claim 30, wherein the lightinjection edge is unpolished.
 32. The glass article of claim 30, whereinthe glass sheet further comprises a second edge adjacent to the lightinjection edge and a third edge opposite the second edge and adjacent tothe light injection edge, wherein the second edge and the third edgescatter light within an angle of less than 12.8 degrees FWHM inreflection.
 33. The glass article of claim 32, wherein the second edgeand the third edge have a diffusion angle in reflection that is below6.4 degrees.
 34. A display device comprising the light guide plate ofclaim
 9. 35. The display device of claim 34, wherein one or more edgesof the light guide plate are illuminated by a light source.
 36. Thedisplay device of claim 35, wherein the light source is selected fromthe group consisting of an LED, CCFL, OLED, and combinations thereof.37. The display device of claim 34, wherein a thickness of the displaydevice is less than 5 mm.
 38. A glass article, comprising: a glass sheetwith a front face having a width and a height, a back face opposite thefront face, and a thickness between the front face and back face,wherein the glass sheet comprises from about 60 mol % to about 80 mol %SiO₂, from about 0.1 mol % to about 15 mol % Al₂O₃, from about 5 mol %to about 12 mol % B₂O₃, and from about 0.1 mol % to about 15 mol %R_(x)O, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2, orR is any one or more of Zn, Mg, Ca, Sr or Ba and x is 1, and wherein theglass produces less than or equal to 2 dB/500 mm absorption.
 39. Theglass article of claim 38, wherein Fe+30Cr+35Ni<about 60 ppm.
 40. Theglass article of claim 38, wherein Fe+30Cr+35Ni<about 40 ppm.
 41. Theglass article of claim 38, wherein Fe+30Cr+35Ni<about 30 ppm.
 42. Theglass article of claim 38, wherein Fe+30Cr+35Ni<about 20 ppm.
 43. Theglass article of claim 38, wherein 0<(R_(x)O—Al₂O₃)<25,−11<(R₂O—Al₂O₃)<11, and −15<(R₂O—Al₂O₃—MgO)<11.
 44. The glass article ofclaim 38, wherein the glass produces less than or equal to 0.5 dB/500 mmabsorption.
 45. The glass article of claim 38, wherein the glassproduces less than or equal to 0.25 dB/500 mm absorption.
 46. A glassarticle comprising: a glass sheet comprising from about 50 mol % toabout 90 mol % SiO₂, from about 0 mol % to about 15 mol % Al₂O₃, fromabout 5 mol % to about 12 mol % B₂O₃, and from about 2 mol % to about 25mol % R_(x)O, wherein R is any one or more of Li, Na, K, Rb, Cs and x is2, or R is any one or more of Zn, Mg, Ca, Sr or Ba and x is 1, andwherein Fe+30Cr+35Ni<about 60 ppm.
 47. A glass article comprising: aglass sheet comprising from about 50 mol % to about 90 mol % SiO₂, fromabout 0 mol % to about 15 mol % Al₂O₃, from about 5 mol % to about 12mol % B₂O₃, and from about 2 mol % to about 25 mol % R_(x)O, wherein Ris any one or more of Li, Na, K, Rb, Cs and x is 2, or R is any one ormore of Zn, Mg, Ca, Sr or Ba and x is 1, and wherein the glass produces2 dB/500 mm or less of light attenuation in the glass sheet.
 48. A glassarticle comprising: a glass sheet comprising from about 50 mol % toabout 90 mol % SiO₂, from about 0 mol % to about 15 mol % Al₂O₃, fromabout 5 mol % to about 12 mol % B₂O₃, and about 0 mol % to about 25 mol% R_(x)O, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2,or R is any one or more of Zn, Mg, Ca, Sr or Ba and x is 1, wherein theglass produces 2 dB/500 mm or less of light attenuation in the glasssheet, and wherein 0<(R_(x)O—Al₂O₃)<25, −11<(R₂O—Al₂O₃)<11, and−15<(R₂O—Al₂O₃—MgO)<11.
 49. The glass article of claim 48, wherein aconcentration of Fe of the glass sheet is <about 50 ppm.
 50. The glassarticle of claim 48, wherein Fe+30Cr+35Ni<about 60 ppm.